NEW:Equilibrium

8/7/2019 NEW:Equilibrium

1/4

Ankur Srivastava The effect of Temperature on Equilibrium 001046029

Chemistry Design Lab: The effect of Temperature onEquilibrium

1 Aim

To determine how a chemical equilibrium is affected by the change in Temperature.

2 Research Question

What is the effect of increasing or decreasing the temperature on the position of equilibrium ofthe endothermic equilibrium reaction in which dinitrogen tetroxide (N2O4) forms Nitrogen dioxide

(NO2) in the forward reaction?

3 Background Knowledge and Hypothesis

Le Chateliers Principle states that if a system at equilibrium is subjected to a small change

the equilibrium tends to shift so as to minimize the effect on the change. The reaction for this

experiment is:

N2O4(g) 2NO2(g)H= 57kJmol1

This is an endothermic reaction, which means that rate of the forward reaction will be increased

by increasing the temperature according to Le Chateliers Principle. Therefore, if the tempera-

ture is increased, it is expected that the equilibrium will be shifted to the products side and if the

temperature is decreased, then the equilibrium will be shifted to the reactants side. Also, temper-

ature is the only factor that can change the value of the equilibrium constant and by increasing

the temperature of the system, the value of the Kcwill increase and vice versa.

The changes in the position of equilibrium can be detected by the nature of this reaction. When

nitrogen dioxide is formed, it is a brownish-yellow colour. As changing the temperature is the

only factor that changes value of the equilibrium constant, the value of the equilibrium constant

at different temperatures of this experiment will show us the position of equilibrium. If the equi-

librium is shifted to the right, it is expected that the value of the Kcwill increase (products over

reactants) and if the equilibrium is shifted to the left then the Kcwill decrease. Using the theory

that has been discussed so far it is expected that:

The concentration of the nitrogen dioxide will increase if the temperature of the system

increases.

The concentration of nitrogen dioxide will decrease if the temperature of the system de-

creases.

Page 1 of 4


2/4


3.1 Variables

3.1.1 Independent

The independent variable will be the temperature of the system in which the reaction is taking

place as this will directly affect the position of the equilibrium and it will be varied as well to give

different readings.

3.1.2 Dependent

The dependent variable will be the concentration of the nitrogen dioxide as it will help in deter-

mining if the equilibrium is being shifted to the left or to the right.

3.1.3 Controlled Variables

1. Temperature of the system.

2. Volume of Dinitrogen Tetroxide.

3. Concentration of Dinitrogen Tetroxide.

4. Time that the reaction was left to take place.

The ways in which these variables will be controlled will be outlined in the Method section.

4 Procedure

4.1 Apparatus Required

1Boiling tube

1Lab Thermometer

At least 5 different containers/tubs

Bunsen burner

1Tape measure

Page 2 of 4


3/4


4.2 Method:

As the dinitrogen tetroxide forms nitrogen dioxide a colour change occurs. Therefore, for this

experiment, it is possible to use spectrophotometric techniques in order to determine the con-

centration of the nitrogen dioxide.

1. First, place a known volume and concentration of dinitrogen tetroxide into a boiling tube

and quickly place a cork over the reaction.

2. Prepare at least 5 different tubs of water, with each at different temperatures. One con-

tainer can even contain ice.

3. Take the temperature of the water using a lab thermometer and then immediately immerse

the lower part of the boiling tube into the water.

4. Wait until the change in colour inside the boiling tube stops, this indicates that the reaction

is completed.

5. Use a spectrophotometer to measure the value of transmittance (T) of the reaction.

6. Use a small torch to shine light onto the boiling tube and use a tape to determine how

much distance the light has traveled before being absorbed. Wrap it around the test tube

to avoid error. The correct length can be calculated later on.

7. Repeat the experiment for the different containers of water.

The value that can be calculated for the concentration of the products can be calculated usingthe equation A bC, where A is absorbance, b is the distance that the light travels before being

absorbed. The absorbance, A can be calculated using the equation A = log(T), where T isthe value for the Transmittance that was measured using a Spectrophotometer.

The value for b can be measured by first determining the diameter of the boiling tube, either

by manufacturing details or using the equation Ddiameter= 2r. Then the circumference can bemeasured and the ratio between half of the circumference and the measured distance should be

first measured. Then the same ratio can be used in order to measure the distance that the light

must have traveled.

By performing these calculations, the values of A and b can be found and the Concentration canbe found. The entire equation is A= EbC, where E is the Equilibrium Constant but even thoughthis is not known, it is a constant value and a pattern that can test the hypothesis can be seen.

4.2.1 Additional notes for Controlling Variables:

1. Temperature: It is expected that heat losses will occur but by measuring the temperature

immediately before immersing half of the boiling tube, this error can be minimized.

2. Volume of Dinitrogen Textroxide: This will be kept constant as a known volume will be

placed into the boiling tube and a cork will be placed on top immediately.

Page 3 of 4


4/4


3. Concentration of Dinitrogen Textroxide: This value was known and was kept constant as

the same reactants were used for all of the experiments.

4. Time that the reaction took place: This was controlled by timing the reaction. After observ-

ing the slowest reaction and timing the reaction (the one with the least temperature), therest of the reactions took place for the same time.

Page 4 of 4

Documents

NEW:Equilibrium