MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

A reaction that can proceed in either direction is considered to be which type of chemical reaction?

a. complete

b. neutralization

c. reversible

d. spontaneous

e. exothermic

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Given the reaction:

Fe(s) + 2HCl(aq) ¨ FeCl₂(aq) + H₂(g)

In this reaction, 5 grams of powdered iron will react faster than a 1-gram piece of solid iron because the powdered iron

a. has less surface area

b. has more surface area

c. is less dense

d. is more dense

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

As the concentration of reacting particles increases, the rate of reaction generally

a. decreases

b. increases

c. remains the same

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

A 1.0-gram sample of powdered Zn reacts faster with HCl than a single 1.0-gram piece of Zn because the surface atoms in powered Zn have

a. higher average kinetic energy

b. lower average kinetic energy

c. more contact with the H⁺ ions in the acid

d. less contact with the H⁺ ions in the acid

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

1. Suppose 10 grams of a water-soluble solid is dissolved in one liter of water. The molar mass of the solid is 100 g/mol. Which of the following methods will probably produce a 0.1 M solution the fastest?

a. placing 10 grams of large crystals in hot water and then stirring.

b. placing 100 grams of small crystals in warm water and then stirring.

c. placing 110 grams of very small crystals in cool water without stirring.

d. placing 10 grams of powder in hot water and then stirring.

e. placing 100 grams of powder in ice water and then stirring.

2. Suppose 20 grams of a water-soluble solid is dissolved in one liter of water. The molar mass of the solid is 100 g/mol. Which of the following methods will probably produce a 0.2 M solution the fastest?

a. placing 20 grams of powder in hot water and then stirring.

b. placing 100 grams of small crystals in warm water and then stirring.

c. placing 100 grams of powder in ice water and then stirring.

d. placing 20 grams of large crystals in hot water and then stirring.

e. placing 120 grams of very small crystals in cool water without stirring.

Correct Answers:

1. d

2. a

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

From the graphs above, which reaction occurs at the slowest rate?

a. Graph A

b. Graph B

c. Graph C

d. Graph D

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

1. From the graphs above, how does increasing temperature affect the following reaction?

a. The reaction rate increases

b. The reaction rate decreases

c. The reaction rate remains the same

2. Citing information presented in the graphs, why is your choice the correct answer?

Correct Answers:

1. b

2. It takes longer time to reach 100% product at high temperatures than it does at low temperature.

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Given the solution at equilibrium:

PbI₂(s) Pb²⁺(aq) + 2I^-(aq)

The addition of which ion will cause a decrease in the concentration of I^-(aq)?

a. Pb²⁺

b. Ca²⁺

c. Li⁺

d. K⁺

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Which event must always occur for a chemical reaction to take place?

a. formation of Ôa precipitate

b. formation of a gas

c. effective collisions between reacting particles

d. addition of Ôa catalyst to the reaction system

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Increasing the temperature increases the rate of a reaction by:

a. lowering the activation energy

b. increasing the activation energy

c. lowering the frequency of effective collisions between reacting molecules

d. increasing the frequency of effective collisions between reacting molecules

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

A catalyst will affect the rate of the forward reaction by changing the

a. activation energy

b. heat of reaction

c. heat of formation

d. potential energy of the products

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Adding a catalyst to a chemical reaction changes the rate of reaction by causing

a. a decrease in the activation energy

b. an increase in the activation energy

c. a decrease in the heat of reaction

d. an increase in the heat of reaction

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Which numbered interval will change with the addition of a catalyst to the system?

a. 1

b. 2

c. 3

d. 4

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

Given the reaction at equilibrium:

A(g) + B(g) C(g) + D(g)

The addition of a catalyst will

a. shift the equilibrium to the right

b. shift the equilibrium to the left

c. increase the rate of forward and reverse reactions equally

d. have no effect on the forward or reverse reactions

Correct Answer: a

P	Chemistry	Standard: 05
Objective: 01. Evaluate factors specific to collisions that affect the rate of chemical reactions.
ILO:

PERFORMANCE ASSESSMENT

Time required: 3-4 periods

Student needs: Baking soda (NaHCO₃) vinegar (5% acetic acid, CH₃COOH)

centigram balance 2-25 mL graduated cylinders

150 mL beaker stopwatch

ice water source hot water source

thermometer graph paper

NOTE: Evaluate each section at the STOP HERE point before proceeding to the next section, this ensures that the students will not make continuous errors that will affect his or her grade.

INTRODUCTION

Instructor demonstration:

1. Take some baking soda and add vinegar to it. Express to the students you are beginning the stopwatch as soon as the vinegar is added, stopping the stopwatch when the reaction is no longer visible, and that you do not shake the beaker.

2. Measure out 10 mL of vinegar, tell the students the temperature. Add 10 mL of hot or cold water to the vinegar, tell the students the new temperature.

Student Experimentation:

EXPERIMENTAL DESIGN

Design a procedure to be completed and evaluated before performing the experiments:

(A) Experiment for the effects of concentration on reaction rates.

Design an experiment to study the effects of vinegar concentration on the rate-reaction with baking soda to form carbon dioxide gas. Start with 0.250 g of baking soda for each trial. Add 20.0 mL of 5%, 2.5% or 1.25% acetic acid concentration to the allotted baking soda. Be sure to clean the beaker between trials! You now know how to correctly make these concentrations! You have also accurately observed the instructorÕs techniques. You can do this! Remember to include more than one trial for each concentration - I know IÕm not always perfect, are you? Write the experimental procedure in a numbered step-by-step sequence. You will be evaluated on the thoroughness of your procedure.

1.

2.

3.

(B) Experiment for the effects of temperature on reaction rates.

Design an experiment to study the effects of vinegar temperature on the rate of baking soda decomposition to carbon dioxide gas. Start with 0.250 g of baking soda for each trial. Your instructor will provide ice water, tap water at about room temperature and hot water. Make a 2.5% acetic acid concentration with these different temperature waters and add 20.0 mL of a specific temperature mix to the allotted baking soda. Be sure to clean the beaker between uses! You now know how to correctly make these concentrations! You have also accurately observed the instructorÕs techniques. You can do this! Remember to include more than one trial for each temperature - I know IÕm not always perfect, are you? Write the experimental procedure in a numbered step-by-step sequence. You will be evaluated on the thoroughness of your procedure.

1.

2.

3.

PERFORMING THE EXPERIMENTS

(A) Experiment to study the effects of concentration on reaction rates.

Construct a table to collect data from your experiment. The table needs to include the acetic acid concentration and the time needed for the reaction to be completed for each concentration trial and an average. Perform the experiment, record the data and graph the data as acetic acid concentration vs. Reaction time. You will be evaluated on your ability to collect and present data accurately.

(B) Experiment to study the effects of temperature on reaction rates.

Construct a table to collect data from your experiment. The table needs to include the acetic acid temperature and the time needed for the reaction to be completed for each temperature trial. Perform the experiment, record the data and graph the data as acetic acid temperature vs. reaction time. You will be evaluated on your ability to collect data accurately.

DATA INTERPRETATION

(A) Experiment to study the effects of concentration on reaction rates.

Based on your data, make a general statement about the effect of concentration of reactants on reaction rate. Evaluation will be on how well the data supports your conclusion.

(B) Experiment to study the effects of temperature on reaction rates.

Based on your data, make a general statement about the effect of concentration of reactants on reaction rate. Evaluation will be on how well the data supports your conclusion.

Ideal Answers & Evaluation (1pt each):

1. In any order, student should have the following observations:

-stopwatch started as soon as vinegar is added to the baking soda

-stopwatch stopped as soon as reaction is no longer evident

-beaker was not shaken or stirred

-temperature of the acetic acid solution is taken after the water is mixed into it

2. In any order, student should have the following observations:

-bubbles are produced when vinegar is added to the baking soda

EXPERIMENTAL DESIGN

Experiment for the effects of concentration on reaction rates.

The procedure should have the following crucial steps in it (1pt each):

-0.250 g of baking soda measured out for each trial

-vinegar dilutions made

-20.0 mL of each dilution measured out

-timing starting and stopping points

-not disturbing the beaker during the reaction process

-the number of repeated trials

Experiment for the effects of temperature on reaction rates.

The procedure should have the following crucial steps in it (1pt each):

-0.250 g of baking soda measured out for each trial

-vinegar dilutions made with corresponding temperatures of water

-temperatures recorded of the vinegar-water mixes

-20.0 mL of each dilution measured out

-timing starting and stopping points

-not disturbing the beaker during the reaction process

-the number of repeated trials

PERFORMING THE EXPERIMENTS

Experiment for the effects of concentration on reaction rates, evaluate the following:

1. Table has correct categories, concentration and reaction time (5pts each)

2. Table has space for each trial (5pts)

3. Table has space for the average of each concentration (2pts)

4. Table has correct acetic acid concentrations listed (1pt)

5. Graph has axis= labeled, time and concentration (3pts each)

6. Graph has units labeled (2pts each)

7. Graph is correctly and evenly spaced (2pts)

Experiment for the effects of temperature on reaction rates, evaluate the following:

1. Table has correct categories, concentration and reaction time (5pts each)

2. Table has space for each trial (5pts)

3. Table has space for the average of each concentration (2pts)

4. Table has correct acetic acid concentrations listed (1pt)

5. Graph has axis= labeled, time and concentration (3pts each)

6. Graph has units labeled (2pts each)

7. Graph is correctly and evenly spaced (2pts)

DATA INTERPRETATION

Experiment for the effects of concentration on reaction rates.

1. As concentration of the reactants increases, so does reaction rate (10pts)

If a student has incorrect data, but correctly interprets this data, award him/her 6pts.

Experiment for the effects of temperature on reaction rates.

2. As temperature of the reactants increases, so does reaction rate (10pts)

If a student has incorrect data, but correctly interprets this data, award him/her 6pts.

TOTAL: 98 points