Pretest 3.1

1. Water is flowing into a sink at a rate of 0.250 L per minute. It is going down the drain at the same rate, so the amount of water in the sink does not change.

Irreversible? Steady state ? Or equilibrium? Explain.

2. A layer of ice and some water underneath are at equilibrium at 0^o C.

1. Will the amount of ice change?

No.

b. Is any freezing occurring? Melting?

Yes, and both reactions are occurring at the same rate. Remember: equilibrium does not mean you necessarily have equal concentrations of reactants and products. Instead, the rates are equal.

H₂O_(s) = H₂O_(l)

c. Would a greater atmospheric pressure affect the equilibrium ? Why ?

  No. No gases are involved.

3. 2 NO₂ = N₂O₄ + heat

brown colourless

a. You place some colourless dinitrogen tetroxide in a cylinder.

What colour will you immediately see, before any reaction occurs, when you pull the piston up, reducing pressure?

As you increase the distance between the molecules, the colour will initially get lighter.

2. When equilibrium is established, what colour will you see?

With less pressure the reverse reaction will be favoured, so the mixture will turn brown.

3. Will the colour's intensity change?

The colour will be darker than the original, but as equilibrium is reestablished the colour will remain constant.

4. Every time two nitrogen dioxide molecules bond to each other, what else is happening at the molecular level ?

One N₂O₄ is decomposing into 2 NO₂’ s.

5. How can you disturb equilibrium so that the mixture goes almost colourless? List two ways.

4. 4 HCl_(g) + O_2(g) = 2H₂O_(g) + 2Cl_2(g) + 112kJ

You want to increase the amount of chlorine gas produced in the above reaction.

1. How would you vary pressure ?

Increase it.

2. How would you vary temperature ?

Decrease it.

3. Would a catalyst help ?

What else could you do ?

5. For exothermic equilibrium reactions ( exothermic from the point of view of the forward reaction ), what do you do to temperature in order to increase the amount of product?

6. a. If a reaction has not yet attained equilibrium, what will be the effect of an inhibitor?

It will slow the rate at which equilibrium is reached

2. Once equilibrium is attained , how will the products be affected by an inhibitor?

Note: the test will also feature two "rerun" questions to keep you sharp. One will involve PV = nRT. The other will involve calculating rates.