Reaction Rates 2
Name: __________________________
Date: __________________________
Catalyst: Answer the catalyst questions here:
Video Investigation: Introduction to Enzymes and Catalysts: What is an enzyme? Why do we need them? What are the four ways
that enzymes speed up chemical reactions?
Notes: Collision Theory of Reactions
 In order to react molecules and atoms must collide.
 They must collide with enough _____________ and at the correct angle to make a reaction happen.
 _____________________ is the minimum amount of energy required to start a chemical reaction.
What is a catalyst and how does it affect reaction rate?
 We know that increasing temperature, reactant concentration, surface area, and pressure all can _______________ the rate
of a chemical reaction.
 A catalyst is a substance that _______________ the reaction rate when it is added to a reaction mixture.
 Catalysts increase the reaction rate by ________________________________________.
 A catalyst is ___________________________________ because it is not used up or changed during the reaction.
 An enzyme is a ______________________ that acts as a catalyst. It is a biological catalyst.
Check for Understanding: A scientist performed the following chemical reaction for the decomposition of hydrogen peroxide:
2 H2O2  2 H2O + O2
In the first trial, oxygen was produced at a rate of 0.001 mol/min. In the second trial, oxygen was produced at a rate of 2 mol/min.
Question: Which trial used a catalyst? How do you know?
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Practice: Read the article and answer the questions. Use complete sentences.
Name: __________________________
Date: __________________________
News Article: Without enzyme catalyst, slowest known biological reaction takes 1 trillion years.
By LESLIE H. LANG
University of North Carolina School of Medicine ---May 5, 2003
All biological reactions within human cells depend on enzymes. Their power as catalysts enables biological reactions to
occur usually in milliseconds. But how slowly would these reactions proceed spontaneously, in the absence of
enzymes – minutes, hours, days? And why even pose the question?
One scientist who studies these issues is Dr. Richard Wolfenden, professor of biochemistry and biophysics and
chemistry at the University of North Carolina at Chapel Hill. In 1998, he reported a biological transformation deemed
"absolutely essential" in creating the building blocks of DNA and RNA would take 78 million years in water without an
enzyme.
In 2003, Wolfenden found a reaction that is 10,000 times slower than that. "Its half-time – the time it takes for half the
substance to be consumed – is 1 trillion years, 100 times longer than the lifetime of the universe. Enzymes can make
this reaction happen in 10 milliseconds."
Wolfenden’s research report highlights the catalytic power of certain enzymes that increase the reaction rate of the
transformation of biochemicals involved in cell signaling pathways. These enzymes help regulate communication
between the body’s cells. Without the enzyme, the uncatalyzed reaction takes 1 trillion years. "This number puts us
way beyond the known universe in terms of slowness," he said. "(The enzyme reaction) is 21 orders of magnitude
faster than the uncatalyzed case.”
Why would we want to know the rate of a biological reaction in the absence of an enzyme?
That information would allow biologists to appreciate what natural selection has accomplished over the millennia in the
evolution of enzymes as prolific catalysts, Wolfenden said. It also would enable scientists to compare enzymes with
artificial catalysts produced in the laboratory.
"Without catalysts, there would be no life at all, from microbes to humans," he said. "It makes you wonder how natural
selection operated in such a way as to produce a protein that got off the ground as a primitive catalyst for such an
extraordinarily slow reaction."
Experimental methods used to observe very slow reactions can generate important information for drug design.
"Enzymes that do a prodigious job of catalysis are, hands-down, the most sensitive targets for drug development,"
Wolfenden said. "The enzymes we studied in this report are fascinating because they exceed all other known enzymes
in their power as catalysts. We’ve only begun to understand how to speed up reactions with chemical catalysts, and no
one has even come within shouting distance of producing their catalytic power."
Wolfenden’s research has influenced rational drug design; findings from his laboratory helped spur development of
ACE inhibitor drugs, now widely used to treat hypertension and stroke.
Questions
1. According to the article, what is activation energy? Based on the article, how does activation energy affect the rate of
a chemical reaction?
2. According to the article, what do enzymes do? Why are enzymes important to cellular processes and life?
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Name: __________________________
Date: __________________________
Practice Instructions: Draw a reaction energy diagram for the breakdown of complex carbohydrates, shown in the box below. This
chemical reaction happens in your mouth. It is aided by an enzyme catalyst called amylase.
In your diagram, be sure to: (1) label all the axes, (2) include a title, (3) label the reactants and products, (4) draw and label the energy
of reaction without the enzyme, (5) draw the energy of reaction with the enzyme, and (6) label the activation energy.
amylase
complex carbohydrates
simple sugars
Additional Practice:
Reaction rate can be measured by
I. rate of formation of the products
II. rate of change in mass of reactants plus products
III. rate of disappearance of the reactants
(a) I only
(c) I and II
(b) I and III
(d) I, II, and III
Which of the following is a unit of reaction rate?
(a) g/mol
(c) mol/L
(b) cm/s
(d) M/s
Which statement describes the effect of concentration
on reaction rate?
(a) Reaction rates increase as products increase.
(b) Reaction rates increase as products increase.
(c) Reaction rates increase as reactants increase.
(d) Reaction rates increase as reactants decrease.
How does increasing temperature increase reaction rate?
(a) It increases the concentration of the reactants.
(b) It increases the collisions between molecules.
(c) It increases the pressure on the reaction.
(d) It increases the fraction of molecules that have
enough energy to react.
A chemical reaction produces 100 mg of a substance per
second at 25°C. If doubling the temperature increases
the rate of production by a factor of 2, how many
milligrams would be produced per second at 50°C?
(a) 50 mg
(c) 200 mg
(b) 100 mg
(d) 400 mg
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