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Comparing Reaction Rate

Description of Activity

Title: Comparing Reaction Rate
Overview: This activity will allow students to investigate reaction rate by varying particle size, temperature, and concentration.
Duration: One 45 minute lab period.
Materials:

Effervescent antacid tablets	Timer or watch with a second hand
Flasks or cups			4M hydrochloric acid
Ice				graduated cylinder
Water				Thermometer
Method of heating water		Magnesium ribbon

Background:

The rate of a chemical reaction is the time required for a given quantity of reactants to be changed to products. Reaction rate usually is expressed in terms of moles per unit time. This rate is affected by several factors including the nature of the reactants, concentration of the reactants, temperature, pressure, and the presence of catalysts.

Teaching and Learning Strategies:

Prerequisite Instruction:

A working definition of reaction rate as a change in concentration divided by time or as a function of time is necessary.

Students must be familiar with the dilution of solutions.

The teacher may wish to divide the class into groups of 2 to 3 students and assign each group to explore 1 of the problems presented. As a variation, the teacher may expand this to use more than 1 class period and have all students investigate each of the problems.

Invitation to Learn

How does temperature, surface area, and concentration affect reaction rate?

Procedure A: How does particle size affect the rate of reaction?

Using effervescent tables, a cup, a graduated cylinder and a stopwatch, give quantitative information in the form of tables and graphs on the relationship between particle size and rate of reaction. One of the problems that must be addressed is how to quantify particle size.

Procedure B: How does temperature affect the rate of reaction?

Using effervescent tablets, a cup, a graduated cylinder, ice, water, stopwatch, and thermometer, provide quantitative information in the form of a table and graph on the relationship between temperature and rate of reaction. You must supply data on at least 5 different temperatures.

Procedure C: How does concentration affect the rate of reaction?

Using magnesium ribbon and 4M hydrochloric acid, provide quantitative information in the form of a table and graph on the relationship between concentration and rate of reaction. You must make at least 5 different dilutions of the acid.

Safe Operating Procedures

Safety goggles and aprons should be worn at all times in the laboratory. Care should be taken when heating water. All chemicals must be disposed of properly. See Flinn Chemical Catalog.

Summary of Learning

1. In each case, what visible indication was there that a chemical reaction occurred?
2. Describe each of the graphs. Do they show linear, hyperbolic, or parabolic relationships? Do they increase or decrease regularly? What other conclusions could be drawn from looking at the graphs?
3. From each graph, give a one sentence conclusion that explains how temperature, concentration, and particle size affect reaction rate. Make a generalization.
4. Why is a fire much easier to start with small pieces of wood rather than one large piece?
5. Based on the information that you collected in the laboratory, why is a car harder to start in the winter than in the summer?

2 multiple choice questions

1. How does temperature affect the rate of reaction?

a. an increase in temperature increases the rate
b. an increase in temperature decreases the rate
c. a decrease in temperature increases the rate
d. temperature does not affect rate

2. How does concentration affect rate of reaction?

a. increasing the concentration tends to decrease the rate
b. decreasing the concentration increases the rate
c. at extremely low concentrations the rate is high
d. concentration does not affect rate

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Updated September 26 1997 by Michelle Dumas