Slide presentation prepared by

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Guinn/Brewer Essentials of General, Organic, and
Biochemistry
CHAPTER 8 CHEMICAL REACTION BASICS

• Slide presentation prepared by
• Martin Brock, PhD,
• Eastern Kentucky University

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CHAPTER 8 Chemical Reaction Basics
DID YOU KNOW?

• 1. What is the main biological molecule
  supplying our bodies with energy?
• 2. What is the similarity between the combustion
  of wood and metabolism occurring in our bodies?
• 3. How can we represent chemical changes?

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CHAPTER 8 Chemical Reaction Basics
DID YOU ANSWER?

• Combustions are chemical changes in which organic
  molecules combine with oxygen, such that water
  and carbon dioxide form. Considerable energy is
  released during these changes. This energy is
  observed as fire if a tree is undergoing
  combustion, but it is also in the metabolism
  driving cellular processes in our bodies when the
  organic molecule is glucose. It may be described
  using the following equation
• C6H12O6 (aq) 6 O2 (g) 6 CO2 (g)
  6 H2O(l) Energy
• glucose oxygen carbon
  dioxide water

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CHAPTER 8 Chemical Reaction Basics
GLUCOSE

• Glucose, an example of a carbohydrate, is the
  primary molecule able to provide our bodies
  cells with energy. Other energy-containing
  dietary molecules include fats and proteins.
• Their changes in our bodies yield energy and
  comprise metabolism. These changes can be
  described and understood using equations.

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CHAPTER 8 Chemical Reaction Basics
OUTLINE

• 8.1 Writing and Balancing a Chemical Equation
• 8.2 Energy and Chemical Reactions
• 8.3 Kinetics Reaction Rates

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CHAPTER 8 Chemical Reaction Basics
CHEMICAL REACTIONS

• All substances have characteristic chemical
  properties.
• These are the tendency to react with certain
  things to form new substances.
• These changes are termed chemical reactions.
• During chemical reactions, bonds between atoms
  are broken and new arrangements of the atoms are
  formed this results in the release or absorption
  of energy.
• In living systems, these reactions are
  collectively termed metabolism.

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CHAPTER 8 Chemical Reaction Basics
RECALL

• The kinetic-molecular view of matter holds that
  atoms and molecules are in constant motion.
• As heat is added to a substance, its molecules
  gain kinetic energy, and thus move faster.
• Temperature is a measure of the average kinetic
  energy of the particles in a substance.
• Molar quantities of a substance can be
  calculated from its mass, using its molar mass as
  a conversion factor.
• Energy is the capacity to do work or transfer
  heat.
• Different types of energy include chemical,
  heat, or mechanical.

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CHAPTER 8 Chemical Reaction Basics
8.1 WRITING AND BALANCING A CHEMICAL EQUATION

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CHAPTER 8 Chemical Reaction Basics
CHEMICAL REACTIONS

• When molecules collide, either they
• just bounce off one another unchanged, or
• there may be enough energy in the collision that
  the atoms recombine in new ways new bonds are
  formed or broken or both.
• This latter possibility results in a chemical
  reaction.

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CHAPTER 8 Chemical Reaction Basics
EXAMPLE OF A CHEMICAL REACTION

• When N2 and O2 interact, they may form a new
  substance, NO, nitric oxide.
• The bonds between atoms of molecular nitrogen
  and oxygen break, and new bonds joining an oxygen
  atom and a nitrogen atom form.
• The starting materials are called reactants and
  the final materials are called products.
  Nitrogen and oxygen are the reactants, and nitric
  oxide is the product.

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CHAPTER 8 Chemical Reaction Basics
LAW OF CONSERVATION OF MASS

• In every chemical reaction, the number and types
  of atoms in the reactants is always the same as
  the number and types of atoms in the products.
• The only difference is in how the atoms are
  joined.
• This is a fundamental principle of nature, and
  is called the law of conservation of mass.

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CHAPTER 8 Chemical Reaction Basics
LAW OF CONSERVATION OF MASS

• Consider the combustion of methane, the blue
  flame on a gas stove. Its reaction can be
  diagram as shown
• Each methane molecule combines with two oxygen
  molecules to form two water molecules and one
  carbon dioxide molecule.
• The same type and number of atoms is present at
  the start as at the finish 1 C, 4 O, and 4 H
  atoms.
• Thus the law of conservation of mass is
  satisfied.

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CHAPTER 8 Chemical Reaction Basics
8.1 WRITING AND BALANCING A CHEMICAL EQUATION

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CHAPTER 8 Chemical Reaction Basics
WRITING CHEMICAL EQUATIONS

• A chemical equation is a short-hand way to
  describe a chemical reaction.
• It identifies all the components of the
  reaction, their relative numbers, and sometimes
  the states of each component.
• Reactants and products are separated by an arrow.

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CHAPTER 8 Chemical Reaction Basics
WRITING CHEMICAL EQUATIONS

• A chemical equation is a short-hand way to
  describe a chemical reaction.
• It identifies all the components of the
  reaction, their relative numbers, and sometimes
  the states of each component.
• Reactants and products are separated by an arrow.

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CHAPTER 8 Chemical Reaction Basics
AN EXAMPLE OF A CHEMICAL EQUATION

• The previous reaction, the combustion of methane
  would be written as follows
• CH4(g) 2 O2(g) CO2(g) 2 H2O(g) heat
• The numbers preceding O2 and H2O are called
  coefficients.
• These indicate the molar ratio of each substance
  present in the reaction.
• If no value is present, such as on the CH4 and
  the CO2, then a coefficient of 1 is implied.
• Coefficients indicate the ratio of moles of each
  component in bulk reactions.
• Thus, one mole of methane reacts with 1 mole of
  oxygen to generate 1 mole of carbon dioxide and 1
  mole of water.
• The letters in parentheses indicate the state of
  the materials. In this case, each component is a
  gas (g), but other equations may indicate the
  presence of a liquid (l), solid (s) or an aqueous
  solution (aq).

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CHAPTER 8 Chemical Reaction Basics
PARTS OF A CHEMICAL EQUATION

• In summary, every chemical equation contains
• Reactants, which are generally listed on the
  left side
• Products, which are generally shown on the right
• A sign separating individual reactants or
  products
• Reaction arrow indicating direction of the
  reaction
• Coefficients showing molar ratios of each
  component
• Physical state, which is sometimes included in
  parentheses following the component

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CHAPTER 8 Chemical Reaction Basics
COMBUSTION REACTIONS

• In combustion reactions, organic compounds react
  with oxygen to form carbon dioxide and water.
• Energy, in the form of heat or light, also
  forms.
• These reactions are often called burning and
  the burning of methane in a gas stove, gasoline
  in a car engine, or tree wood during a forest
  fire are all examples of combustion reactions.

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CHAPTER 8 Chemical Reaction Basics
COMBUSTION OF GLUCOSE

• In metabolism in biological cells, the sugar
  glucose, in aqueous solution, is used as a fuel
  in a process similar to combustion.
• Water vapor, carbon dioxide gas, and energy are
  all formed
• Note that the oxygen we breathe is an essential
  component of this reaction.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEMS

• For each of the following chemical equations,
• i. C3H8 (g) 5 O2 (g) 3 CO2 (g)
  4 H2O (l)
• ii. C4H6 (g) 2 H2 (g) C4H10 (g)
• iii. Ba(OH)2 (aq) 2 HCl (aq)
  BaCl2 (aq) 2 H2O (l)
• a. Indicate the reactant(s).
• b. Indicate the product(s).
• c. Indicate the ratio in which the reactants and
  products react.
• d. Indicate the physical state of each reactant
  and product.
• e. Which reaction above represents a combustion
  reaction? Explain.

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CHAPTER 8 Chemical Reaction Basics
BALANCING CHEMICAL EQUATIONS

• Because mass is conserved in chemical reactions,
  chemical equations must be written to indicate
  this.
• Coefficients are used to show conservation of
  every atom in an equation.
• Selecting coefficients for each formula to match
  numbers of atoms in reactants and products is
  called balancing the chemical equation.

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CHAPTER 8 Chemical Reaction Basics
GUIDELINES FOR BALANCING EQUATIONS

• 1. Assess the equation.
• Determine the number and types of atoms in each
  reactant and product. If the numbers are not
  equal on both sides, the equation is not
  balanced.
• 2. Balance the equation one atom type at a time
  by inserting coefficients.
• Systematically insert coefficients, and see if
  the equation is balanced.
• Never change the subscripts!
• Best to wait until the end to balance any
  component present in multiple forms on one side
  of the equation.
• 3. Check that the coefficients cannot be divided
  by a common divisor.
• Fractions may be used temporarily, but then
  multiply every coefficient by the divisor so as
  to have only integers for coefficients.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEM

• Balance the following chemical equations by
  inserting the appropriate coefficients
• a. ___CH2O2 (l) ___O2 (g)
  ___ CO2 (g) ___ H2O (g)
• b. ___N2O5 (g) ___NO2 (g) ___ O2
  (g)
• c. ___C6H12O2 (l) ___ O2 (g)
  ___CO2 (g) ___ H2O (g)
• d. ___CaCO3 (s) ___HCl (aq) ___
  CO2 (g) ___ H2O (l) ___ CaCl2 (aq)

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CHAPTER 8 Chemical Reaction Basics
REACTION STOICHIOMETRY CALCULATIONS

• Using a balanced chemical equation, it is
  possible to calculate how many grams of product
  form from a given number of grams of reactant.
• These calculations are known as stoichiometry.
• Using molar masses as conversion factors, and
  the molar ratios of products and reactants given
  by the coefficients, these calculations are
  straightforward.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEM

• How many grams of carbon dioxide are formed when
  10.0 g of glucose undergoes combustion to form
  carbon dioxide and water? Begin by writing the
  complete balanced equation.

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CHAPTER 8 Chemical Reaction Basics
8.2 ENERGY AND CHEMICAL REACTIONS

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CHAPTER 8 Chemical Reaction Basics
BIOENERGETICS

• Bioenergetics is the study of energy associated
  with living processes.
• Energy for living comes from chemical reactions
  acting on food in our diet in cells in our body.
• Chemical energy in foods is a form of potential
  energy stored in the bonds in key biomolecules
  such as carbohydrates, fats, and proteins in our
  bodies.

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CHAPTER 8 Chemical Reaction Basics
UNITS OF ENERGY

• Calories and joules are the units of energy most
  commonly used.
• 1 calorie (cal) is the amount of heat needed to
  raise 1 g of water by 1?C.
• 1 kilocalorie (kcal) is 103 calories.
• Food Calories are equal to kilocalories.
• Note the uppercase C in food Calories.
• 1 cal 4.184 joules, exactly.

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CHAPTER 8 Chemical Reaction Basics
COMPARING UNITS

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEM

• Using the conversions in the previous table,
  convert the following units into calories. More
  than one step may be required when there is not a
  direct conversion.
• a. 5.79 kcal
• b. 48.8 J

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CHAPTER 8 Chemical Reaction Basics
HEAT ENERGY

• Energy is transferred in chemical reactions,
  often in the form of heat energy.
• Heat energy is produced in combustion reactions,
  such as the burning of propane in an outdoor
  grill
• C3H8 (g) 5 O2 (g) ? 3 CO2 (g) 4
  H2O (g) Heat Energy
• Heat energy transferred is referred to as the
  change in enthalpy, ?H, of the reaction.
• Other energy may also be released, such as light
  or mechanical energy.

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CHAPTER 8 Chemical Reaction Basics
EXOTHERMIC AND ENDOTHERMIC REACTIONS

• While some reactions release heat, others absorb
  heat.
• In an exothermic reaction, heat is released to
  the surroundings, which become hotter.
• In an endothermic reaction, heat is absorbed
  from the surroundings, which become cooler.
• Heat is released or absorbed as a consequence of
  bonds breaking and reforming during a chemical
  reaction.
• Energy must be absorbed to break a bond.
• Energy is released in forming a new bond.
• Different types of bonds have different levels
  of energy.
• This is called bond energy, and the total change
  in bond energy during a reaction accounts for ? H.

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CHAPTER 8 Chemical Reaction Basics
ENERGY DIAGRAMS

• Energy diagrams can be used to show the
  difference between a) exothermic and b)
  endothermic reactions.
• In exothermic reactions, ? H is negative and in
  endothermic reactions, ? H is positive.

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CHAPTER 8 Chemical Reaction Basics
ENERGY IS ALWAYS CONSERVED!

• In the energy diagram, energy going into the
  reaction is balanced by the change in energy
  level of the products, and vice-versa.
• This is a consequence of the First Law of
  Thermodynamics, which states that energy can
  never be created nor destroyed.
• Therefore, if a reaction is exothermic, its
  reverse reaction will be endothermic the
  numerical value of ?H will be the same for both
  reactions, but its sign ( or ?) changes.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEMS

• For each of the following reactions, indicate
  whether it is an endothermic or an exothermic
  reaction and provide an energy diagram for each.
  
• a. 8 H2S (g) 8 H2 (g) S8 (s) heat is
  absorbed
• b. 2 CO2 2 CO O2 ? H 566 kJ

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CHAPTER 8 Chemical Reaction Basics
CALORIMETRY

• Calorimetry is the measurement of ? H using an
  instrument called a calorimeter.
• Energy content of combustible materials is
  measured this way.
• Samples are placed in an inner chamber (the
  bomb).
• It is filled with oxygen and sealed.
• This is surrounded by water, then ignited.
• The heat released is absorbed by the water.
• Temperature difference of the water before and
  after the reaction is used to calculate ? H.

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CHAPTER 8 Chemical Reaction Basics
MEASURING THE CALORIC CONTENT OF FOODS

• The data from the calorimeter may be used to
  record nutritional information on the foods you
  purchase.
• The energy value of foods to our bodies is the
  same as the energy value determined by
  calorimetry.

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CHAPTER 8 Chemical Reaction Basics
WHAT IS THE CALORIC CONTENT OF FOOD?

• The results of calorimetry show that while
  carbohydrates and proteins have similar caloric
  content (Cal/g), fats have much more.

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CHAPTER 8 Chemical Reaction Basics
CALCULATING DIETARY CALORIES

• The total calories in a food item can be
  calculated from this data. Nutritional labels
  tell how much of each food type is present.
• Calories provided by
• fat grams of fat ? 9 Cal/g
• carbohydrate grams of carbohydrate ? 4
  Cal/g
• protein grams of protein ? 4 Cal/g
• Total Calories Calories fat Calories
  carbohydrate Calories protein

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEMS

• 1. A piece of angel food cake contains 33 g of
  carbohydrate, 3 g of protein, and 0 g of fat.
  How many total Calories does a piece of angel
  food cake contain?
• 2. A cup of pasta contains 32 g of carbohydrates,
  5 g of protein, and 1 g of fat. How many total
  Calories does a cup of pasta contain?

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CHAPTER 8 Chemical Reaction Basics
METABOLISM OVERVIEW

• Biochemical reactions are reactions occurring in
  the cells in our body.
• They are usually found as sequences of reactions
  called biochemical pathways.
• The two classes of biochemical pathways are
• Catabolic pathways
• These break down large dietary molecules such as
  carbohydrates, proteins, and fats into small
  products such as carbon dioxide and water.
• Anabolic pathways
• These build up large molecules such as proteins
  and DNA from smaller building blocks in our diet.

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CHAPTER 8 Chemical Reaction Basics
METABOLISM AND ENERGY

• Generally, catabolism releases energy and
  anabolism absorbs energy.

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CHAPTER 8 Chemical Reaction Basics
HOW IS BIOLOGICAL ENERGY TRANSFERRED?

• Biochemical energy is transferred in the form of
  chemical energy to and from specialized energy
  carrier molecules.
• The most important of these energy transfer
  molecules is adenosine triphosphate, ATP.
• ATP is often referred to as the energy currency
  of the cell.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEM

• Indicate whether each of the following processes
  is catabolic or anabolic. Indicate whether each
  releases energy or absorbs energy overall.
•  
• a. Building muscle protein from amino acid
• molecules
• b. A bear burning fat during hibernation
• c. Storing glucose in the form of large
  polymers,
• known as glycogen

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CHAPTER 8 Chemical Reaction Basics
8.3 KINETICS REACTION RATES

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CHAPTER 8 Chemical Reaction Basics
CHEMICAL KINETICS

• Chemical kinetics is the study of how fast
  reactions proceed.
• Reaction rates are measured by following
  concentration changes of product or reactant over
  time.
• Some reactions occur very fast, in less than a
  second.
• Other reactions may take place over millions of
  years.
• Biochemical reactions take place in an
  intermediate time frame, just right for
  biological processes.

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CHAPTER 8 Chemical Reaction Basics
ACTIVATION ENERGY

• Reaction rates depend on the activation energy,
  EA, of a reaction.
• Activation energy is the amount of input energy
  needed to initiate a reaction.
• If the amount of energy in the collision of two
  reactant molecules is less than this amount,
  bonds wont break and there wont be enough
  energy for the reaction to take place.
• If the energy level is high enough, the
  re-forming of new bonds provides enough energy to
  sustain the reaction.

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CHAPTER 8 Chemical Reaction Basics
ACTIVATION ENERGY AS BARRIER

• EA is like a hill to be climbed over. It
  requires some energy to reach the top, but you
  can coast down the other side.

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CHAPTER 8 Chemical Reaction Basics
ACTIVATION ENERGY AND ?H

• The enthalpy (? H) for a reaction depends only on
  the reactant energy at the start and the product
  energy at the end, and is not influenced by the
  activation energy.

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CHAPTER 8 Chemical Reaction Basics
ACTIVATION ENERGY AND ?H

• If the activation energy is low, then most
  collisions result in a chemical reaction, so a
  reaction goes fast.
• If the activation energy is high, most
  collisions are not productive, so reaction is
  slow.
• Reaction diagrams showing activation energy
  allow us to predict the rate of a chemical
  reaction.

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEM

• Draw energy diagrams for two endothermic
  reactions with different activation energies.
• a. Label each axis.
• b. Indicate which reaction would proceed at the
  
• faster rate.
• c. Indicate the distance on the y-axis that
• represents the activation energy,
  EA.
• d. Label ? H using a double-headed arrow
  parallel
• to the y-axis.
• e. Label the position on the graph that
  represents
• the reactants.
• Do the same for the products.

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CHAPTER 8 Chemical Reaction Basics
practice

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CHAPTER 8 Chemical Reaction Basics
WHAT AFFECTS THE RATE OF A REACTION?

• Reaction rates are affected by several factors
• concentration of reactants
• temperature of the reaction
• presence of a catalyst
• Varying these allows scientists (or biological
  systems) to control chemical reactions.

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CHAPTER 8 Chemical Reaction Basics
REACTION RATE AND CONCENTRATION

• Reaction rates decrease as reactant concentration
  decreases.
• Lower levels of reactants mean fewer collisions
  per second, so the reaction proceeds slower.

• The following equation describes the
  decomposition of N2O5 
• 2 N2O5 (g) 4 NO2 (g) O2 (g)
• As N2O5 gets used up, less of it is available to
  react, collisions occurless often so the rate of
  its disappearance decreases. The graph
  illustrates this initially, the line is
  steeper, but it become less steep as the reaction
  progresses. 

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CHAPTER 8 Chemical Reaction Basics
REACTION RATE AND TEMPERATURE

• Because molecules are moving faster at a higher
  temperature, there are more collisions per
  second.
• This results in a greater reaction rate.
• Greater particle velocities also mean a greater
  amount of energy is transferred each time a
  collision occurs.
• This results in a greater chance for a
  productive chemical reaction.
• At lower temperatures, collisions may not be
  strong enough to result in a chemical reaction.
• It is generally the case that for every 10?C
  change in temperature, the reaction rate doubles.

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CHAPTER 8 Chemical Reaction Basics
DOES TEMPERATURE MATTER?

• One reason we refrigerate our foods is that the
  lower temperature means the chemical reactions
  causing foods to spoil are slowed down.
• In biochemical systems such as our body, the
  fairly constant temperature of 37?C means
  temperature is usually not a variable in
  biochemical reactions.

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CHAPTER 8 Chemical Reaction Basics
REACTION RATE AND CATALYSTS

• A catalyst is a substance that increases the
  rate of a chemical reaction by lowering the
  activation energy for the reaction.
• By reducing the activation energy, a given
  collision is more likely to cause a chemical
  change, so the reaction occurs more quickly.
• Catalysts do not effect the enthalpy, ?H, of the
  reaction, as the energies of reactants and
  products are not changed.

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CHAPTER 8 Chemical Reaction Basics
ENZYMES ARE BIOCHEMICAL CATALYSTS

• Chemical reactions in our body are not much
  affected by temperature, as it is a fairly
  constant 37?C.
• Special biological molecules called enzymes work
  as catalysts to speed up specific reactions.
• Enzymes may speed up reactions by factors
  ranging from 105- to 1017-fold.
• Enzymes are of such high importance that if one
  is missing or damaged, serious disease can
  result.

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CHAPTER 8 Chemical Reaction Basics
ENZYMES ON A ENERGY DIAGRAM

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CHAPTER 8 Chemical Reaction Basics
PRACTICE PROBLEMS

• For the following reactions, state whether the
  indicated change in conditions would increase
  or decrease the rate of the reaction. Explain
  why.
• a. 2 H2O2 (aq) 2 H2O (l) O2 (g)
• More H2O2 is added to the reaction.
• b. CO (g) NO2 (g) CO2 (g) NO (g)
• The temperature is reduced from 4300C to 3300C.
• c. 2 H2O2 (aq) 2 H2O (l) O2 (g)
• Sodium iodide, a catalyst, is added to the
  reaction.
• 2. Draw an energy diagram showing an exothermic
  reaction with and without a catalyst.

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CHAPTER 8 Chemical Reaction Basics
practice

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CHAPTER 8 Chemical Reaction Basics
SUMMARY OF MAIN CHAPTER POINTS, P1

• Writing and Balancing a Chemical Equation
• Chemical reactions break bonds between atoms in
  compounds and form new ones.
• Chemical reactions either release or absorb
  energy.
• A chemical equation represents a chemical
  reaction.
• The law of conservation of mass states that
  matter is conserved during a chemical reaction.
• Balancing a chemical equation involves inserting
  whole number coefficients so that the number of
  each type of atom is the same on the reactant
  side as on the product side.

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CHAPTER 8 Chemical Reaction Basics
SUMMARY OF MAIN CHAPTER POINTS, P2

• Energy and Chemical Reactions
• Energy is the capacity to do work or to transfer
  heat.
• Energy can be measured in units of Joules,
  calories, and kilocalories.
• The energy transferred in a chemical reaction is
  often in the form of heat.
• Most chemical reactions absorb or release heat.
• The change in enthalpy, ? H, is a measure of the
  heat released or absorbed in a chemical reaction.
• An exothermic reaction releases heat energy into
  the surroundings. ? Hlt0.
• An endothermic reaction absorbs heat energy from
  the surroundings. ? Hgt0.
• Calorimetry measures enthalpy changes in
  reactions, using a calorimeter.
• Metabolism consists of biochemical pathways.
• Catabolic pathways convert large molecules into
  smaller molecules to release energy.
• Anabolic pathways convert small molecules into
  larger ones so absorb energy.
• Adenosine triphosphate, ATP, is the main energy
  currency of the cell.

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CHAPTER 08 Chemical Reaction Basics
SUMMARY OF MAIN CHAPTER POINTS, P3

• Kinetics Reaction Rates
• Chemical kinetics is the study of reaction
  rates.
• A chemical reaction can proceed when reactant
  molecules collide with enough energy.
• The minimum energy needed for a chemical
  reaction to proceed is the activation energy, EA.
• EA determines the rate of the reaction the
  higher EA, the slower the reaction.
• The rate of the reaction can be influenced by
  the concentration of reactants, the temperature
  of the reaction, or the presence of a catalyst.
• The higher the concentration of reactants, the
  faster the reaction.
• As the temperature increases, the rate also
  increases.
• A catalyst lowers EA, thus increasing the rate
  of the reaction.
• Biological catalysts are called enzymes.