Equilibrium Between NO2 and N2O4

1. What substance was in each test tube?  Provide a ball and stick model.

In each test tube, there was nitrogen dioxide and dinitrogen tetroxide.

Nitrogen Dioxide

Dinitrogen Tetroxide-Molecule Struture

Dinitrogen Tetroxide

2. What happens when you place the test tube in boiling water into the ice water? What process is favored by the changes?  What’s occurring at a faster rate?  What is the change in concentration?

When you place the test tube in boiling water into the ice water, the orangish NO2 gas disappears, and is replaced with colorless N2O4 gas. The formation of N2O4 is favored by the changes. The rate of the production of N2O4 is occurring at a faster rate than the rate of production of NO2, which is why the tube color turns from orange to clear. So, the concentration of N2O4 increases while the concentration of NO2 decreases.

3. What happens when you place the test tube in ice water into the boiling water?  What process is favored by the change?  What’s occurring at a faster rate?  What is the change in concentration?

When we placed the test tube into the boiling water after it sat in ice water, the type of gas produced changes. The color of the gas changes from clear to orangish yellow NO2 which is favored because the formation of NO2 gas is endothermic. At this point, the production of NO2 is occurring at a faster rate than the break down of N2O4, which is why the concentration of NO2 increases and the concentration of N2O4 decreases, accounting for the color change.

4. What is the balanced equation (including enthalpy)?

2NO2<—> N2O4                           Enthalpy: -58.0 kJ/mol

5. Explain your observations of the reversals in terms of LeChatelier’s principle.

Our observation makes sense based on LeChatelier’s principle that states that when a system at equilibrium is subjected to change, the system readjusts it self to attempt to counteract the effect of the change. In our lab, when the temperature was changed, the reversible reaction rates adjusted in order to accommodate the change,  as the system tried to maintain equilibrium.

6. What is happening within the test tube at room temperature?  How is it related to the hot and cold test tubes?

At room temperature, the test tube is at equilibrium. It is related to the hot and cold test tubes because the change in temperature affects which side of equilibrium the test tube is on (in regards to enthalpy). The direction of the reaction and type of gas produced is based on whether the enthalpy of the reaction is positive or negative. The positive or negative enthalpy value determines which reaction is favored at a given temperature.

IMG_2062IMG_2059

Sources:

http://en.wikipedia.org/wiki/Le_Chatelier%27s_principle

http://www.shutterstock.com/s/nitrous/search.html?page=1&inline=214524664

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