Procedural Tips:

Using the Bunsen Burner

FAQ:

Why do I have to wear safety goggles?

Introduction/Goals:

Introduction:

In this lab you will study the effects of reactant concentration and temperature of reaction rates and demonstrate how the equilibrium of a chemical reaction may be shifted by changed the concentration of products or reactants.

Goals:

	Describe the factors affecting reaction rate
	Explain how changing the ratio of products to reactions will shift the equilibrium of a reaction.

Background:

The rate of a chemical reaction is dependent upon the number of effective collisions that the reacting molecules undergo. An effective collision is one where the colliding molecules have the proper orientation and enough energy (force) for the reaction to occur. Factors that increase the number of effective collisions are the amount of reactants, the temperature, and the presence of a catalyst.

Increasing the concentration of reactants will increase the reaction rate because there will be a greater probability of an effective collision between molecules when there are more molecules present.

When the temperature increased the kinetic energy of molecules is increased. This increase in kinetic energy increases the frequency of collision and also the speed of the collision. The number of effective collisions increases because of both of these factors.

A catalyst is a substance that increases the rate of a chemical reaction but is not used up in the reaction. A catalyst speeds up a reaction by providing the reaction an alternate pathway by which to react. The alternate pathway has a lower activation energy. The activation energy is the energy needed to start a spontaneous reaction. If the activation energy is lowered, more of the collisions between reactant molecules will have sufficient energy for the reaction to occur.

Most reactions are reversible. In a reversible reaction, the reaction can proceed in both directions. In other words, the products may be considered to be reactants if a reaction takes place in the opposite direction. After a period of time, the rate of the forward reaction equals the rate of the reverse reaction. The reaction has now reached a state of equilibrium. At equilibrium it appears that the reaction has stopped. However, this is not the case. The equilibrium is dynamic, meaning that the rate of product formation is equal to the rate of reactant re-formation.

LeChâtelier's principle states that when stress is applied to a system in equilibrium, the equilibrium shifts to relieve the stress. Stress is a change in concentration of products or reactants, pressure, or temperature. For example, if you increase the concentration of reactant in a system at equilibrium, the equilibrium will shift toward the products (to the right). In other words, more product will be formed. Conversely, if you decrease the reactant concentration, the equilibrium shifts to the left and more reactants are formed.

 

Pre-lab:

Read the introductory material on the webpage.

Read Experiment Seven in the laboratory manual.

Answer the pre-lab study questions for Experiment Seven.

You are encouraged to do the Application Questions at the end of Experiment Seven before coming to lab.

Additional Questions:

1. Indicate whether the following changes will increase or decrease the rate of this chemical reaction: 2 CO + O₂ ® 2 CO₂
1. Addition of CO:                                  
2. Lowering the temperature of the reaction mixture:                                   

2. How will addition of CS_2(g)   affect the equilibrium of the following reaction?

CH_4(g) + 2 H₂S_(g) + heat  CS_2(g) + 4 H_2(g)                                               

3. Substances burn more rapidly in pure oxygen than in air. Why?
4. How will an increase in temperature affect the equilibrium of the following reaction?   CH_4(g) + 2 H₂S_(g) + heat  CS_2(g) + 4 H_2(g)                                        
5. Answer Question 7.55 in the McMurray textbook.

 

Supplies and Chemicals:

	Test tubes
	Test Tube racks
	Spatula
	Thermometer
	150 mL beakers
	250 mL beakers
	10 and 100 mL graduated cylinders
	Droppers
	Ice
	0.02 M potassium iodate
	0.1 M sodium sulfite-starch
	hydrogen peroxide
	MnO2
	0.1 M acetic acid
	methyl orange
	sodium acetate
	bromthymol blue
	0.1 M HCl
	0.1 M NaOH

Safety Precautions:

SAFETY GOGGLES MUST BE WORN AT ALL TIMES DURING THE LABORATORY

Hydrochloric acid (HCl) is a strong acid. If you get any on your skin, wash it off immediately with cold water. If any HCl is splashed in your eyes, wash immediately at the eye fountain. Review the first acid procedures for chemical burns to the skin and eyes.

Use caution when boiling water.

Waste Disposal:

There are no specific waste disposal instructions