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## Demonstration: Introduction to Reaction Rates

In this demonstration you will observe the following chemical reaction:

CaCO3 + 2HClCO2 + H2O + CaCl2

In this reaction a solid reacts with a solution to produce a gas, water, and a dissolved salt. The visible sign of the reaction is the formation of the gas. There are four 125 mL flasks set up with calcium carbonate already measured into them. Four beakers stand at the ready to be poured into the flasks. Your task is to look at the initial conditions for each flask and predict what you will observe. Here are the amounts of each reactant:

 A B C D Calcium Carbonate (CaCO3) 25 g (chips) 25 g (chips) 10 g (powder) 10 g (powder) Hydrochloric Acid (HCl) 60 mL 1 mol/L 10 mL 6 mol/L 60 mL 1 mol/L 10 mL 6 mol/L

In all experiments the initial temperature is the same. The purpose of the experiments is to explore two factors that affect the rate at which a reaction occurs. A simple way to think about the rate of reaction is to think about measuring the number of molecules that react per second.

Questions
Before the experiments:
1. There are two forms of calcium carbonate being used in these experiments. Describe them.
Which form has more molecules available to react when immersed in liquid? Explain.
2. Only 10 mL of the more concentrated acid is being used, as compared with 60 mL of the less concentrated acid. What effect will this have on the observed rate of reaction?
3. Consider the different concentration of hydrochloric acid in the experiments. What effect will the different concentrations have? Explain.
4. How will you be able to visually compare the rates of reaction between the flasks?
5. Put these experiments in order from fastest reaction to slowest reaction from left to right:
(fastest)                                                                      (slowest)

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After the experiments:
1. What effect does the size of solid particles have on the rate of reaction? Justify your answer using observations from the demonstration.
2. What effect does solution concentration have on the rate of reaction? Justify your answer using observations from the demonstration.
3. Did the volume of acid ultimately make a difference in the rates you observed? Explain.
4. You know, of course, that molecules have a higher average speed at higher temperatures. What effect would a higher temperature have on the rate of reaction? Explain.

Last Updated: Feb 12, 2018
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