Factors Affecting Rate of Reactions Objective : Study the factors affecting the

Question

Factors Affecting Rate of Reactions

Objective : Study the factors affecting the rates of reactions.

Procedure :

Part 1 - nature of reactants 1

(1) Obtain 5 test tubes and number them #1 to #5. For each, place 1-cm strip of Mg.

(2) Add 1mL of 2M sulfuric acid to #1, 1mL of 2M hydrochloric acid to #2, 1mL of 2M nitric acid to #3, 1mL of 2M phosphoric acid to #4, 1mL of 2M acetic acid to #5.  

(3) Note the rates.

* Write a balanced equation between Mg and acetic acid including states.

Mg + 2HC2H3O2 —> Mg(C2H3O2)2 + H2

Part 2 – nature of reactants 2

(4) Obtain 3 test tubes and place 1mL of 6.0M HCl in each.

(5) Add 1cm polished strips of Mg to the first, Zn to the second and Cu to the third.

(6) Note the rates.

* Write a balanced equation between HCl and Mg. Make sure to include states.

Mg + 2HCl —> MgCl2 + H2

Part 3 – Concentration of reactants

(7) Obtain 3 test tubes and number them #1 to #3. For each, place on 1-cm strip of Mg.

(8) Add 1mL of 1M sulfuric acid to #1, 1mL of 3M sulfuric acid to #2 and 1mL of 6M sulfuric acid to #3.

(9) Note the rates.

* Write a balanced equation between Mg and sulfuric acid including states.

          Mg + H2SO4 ———> MgSO4 + H2

Part 4 - Surface area

(10) Obtain 2 test tubes. Place one marble chip (CaCO3) into one test tube and about same amount of crushed marble chips into the other test tube.

(11) Add 1mL of 6.0M HCl to each test tubes.

(12) Note the rates

* Write a balanced equation between CaCO3 and HCl including states.

CaCO3 + 2HCl ———> CaCl2 + CO2 + H2O

Part 5 – Temperature

(13) Obtain 3 test tubes and add 1mL of 6.0M HCl to all three.

(14) Place one test tube in an ice bath, the second in a warm water bath, and the third in a tap water. Wait 5 minutes.

(15) To each test tube, add a piece of Zn.

(16) Note the rates.

* Write a balanced equation between Zn and HCl including states.

          Zn + 2HCl ———> ZnCl2 + H2

Part 6 – Catalyst

(17) Obtain 2 test tubes and add 1mL of 3% H2O2 to both.

(18) Add few grains of MnO2 to one of the test tubes.

(19) Note the rates.

* Write a balanced equation for decomposition of H2O2 including states.

          2H2O2 ———> 2H2O +O2

Postlab Questions:

List and describe the factors that affect the rate of a reaction.

Rate is quantitative with unit of M/sec. We are not measuring anything quantitative for this lab. How did you study the rate for this lab?

How did you note the rate for each part? i.e. Color changing to red? Test tube getting hot?

How does the rate of a reaction differ from equilibrium for a reaction.

What would happen to the rate in part 1, if you use cubic chunks of Mg instead of Mg ribbon of same amount? Why?

In part 6, what was the purpose of adding manganese (IV) oxide, MnO2? Draw a reaction energy diagram showing the difference between the reaction with MnO2 and without MnO2? Include activation energy, heat of reaction, reactants and products, and label your x and y axes.

Summary :

For each part, list the reactions in increasing rate.  

Example:

      For part 2, Mg + HCl    < Cu + HCl   <   Zn + HCl (Zn being the fastest reaction)

                   Just writing: “Mg < Cu < Zn”   is not complete!

Need help with post lab

Explanation / Answer

The first four parts would be answered as per rules.

1. Factors affecting the rate of a reaction -

a. Rate depends on the acidic strength.

Acidic strength order from weak to strong : Acetic acid < Phosphoric acid < Nitric acid < Hydrochloric acid < Sulphuric acid.

Hence the reaction rate follows the order  CH3COOH + Mg < H3PO4 + Mg < HNO3 + Mg < HCl + Mg < H2SO4 + Mg.

b. Rate depends on the activity of the metals.

More the reactivity of the metal, faster the reaction, higher the reaction rate.

Reactivity order : Cu < Zn < Mg

Rate of reaction : Cu + HCl < Zn + HCl < Mg + HCl

c. Rate depends on the concentration.

Higher the concentration, more the collisions between molecules, faster the reaction, more the reaction rate.

Concentration increases as : 1M H2SO4 < 3M H2SO4 < 6M H2SO4

Reaction rate : 1M H2SO4 + Mg < 3M H2SO4 + Mg < 6M H2SO4 + Mg

d. Rate depends on the surface area.

Higher the surface area, greater the number of collisions, higher the reaction rate.

Powdered substances have higher surface area and hence has a higher reaction rate than solid substances.

Hence crushed marble chips will have higher rreaction rate than one marble.

e. Rate depends on the temperature.

Higher the temperature, higher the number of collisions, more the reaction rate.

2. Rate is defined as the speed of a reaction i.e how fast a reaction is carried out. So through qualitative analysis like analysis of colour, change in temperature of test tube, changes in pH, liberation of gas etc the rate can be studied.

3. Rate determination:

Measuring the volume of H2 gas released when metals react with acids and change in temperature of the test tube.

4. Rate of reaction is how fast a reaction occurs.

Whereas equilibrium is comparing the products and reactants in a reversible reaction. At equilibrium both the forward (reactant to product) and the backward (products to reactants) reactions are occurring at the same rate. So the concentration of product and reactant will remain the same.

Changes in concentration, temperature and pressure can disturb the equilibrium and produce either more reactant or product. However rate of a reaction cannot be changed to increase or decrease concentration of either reactant or product.

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