7.1 Equilibrium Systems

Question 1

Do all chemical reactions proceed to completion?

Answer 1

No

Question 2

Define Chemical Equilibrium

Answer 2

State of reaction where reactants and products have reached constant concentrations in a closed system

Question 3

What’s a forward reaction

Answer 3

Left to right (reactants to products)

Question 4

What’s a reverse reaction

Answer 4

Right to left (products to reactants)

Question 5

Define closed system

Answer 5

A system where matter cannot be transferred between systems and surroundings, but energy can

Question 6

How is bromine an example of a physical equilibrium (also applies to water)

Answer 6

Bromine has volatile energy to evaporate, and its vapor collides with its liquid to become liquid bromine. The rate of condensation is equal to the rate of evaporation, making it an equilibrium with no net change in liquid and gas present.

Question 7

How is decomposition of HI a chemical equilibrium

Answer 7

As [HI] decreases the reverse reaction rate increases and eventually both rates become equal and their concentrations become constant.

Question 8

Are all chemical equilibriums dynamic?

Answer 8

Yes

Question 9

What is the equilibrium position

Answer 9

The relative concentrations of reactants and products at equilibrium

Question 10

In equilibrium, do the concentrations of reactants ever reach 0?

Answer 10

No

Question 11

What are reversible reactions

Answer 11

Reactions that can proceed in both forward and reverse directions

Question 12

Is the equilibrium position the same regardless of the direction it was achieved in?

Answer 12

Yes

Question 13

What are the 5 characteristics of an equilibrium

Answer 13

1) equilibrium is dynamic
2) it is in a closed system
3) concentrations of all reactants and products remain constant at equilibrium
4) macroscopic properties do not change
5) can be achieved in either direction

Question 14

Explain how NO2 <-> N2O4 is an example of a reaction not proceeding to completion

Answer 14

NO2 is a dark gas whilst N2O4 is colorless. In a closed system the vial gets lighter but never colorless even when it reaches equilibrium. The reactant never ran out, so it does not proceed to completion.

Question 15

In dynamic equilibrium, the rate of the forward reaction is _____ to the rate of the reverse reaction

Answer 15

Equal

Question 16

What does a dashed line on a chemical reaction graph indicate

Answer 16

Equilibrium was reached and all concentrations will remain constant

Question 17

When concentrations of reactants and products are not changing, is the reaction always at equilibrium? Use ammonia synthesis to explain (N2 + 3H2 <-> 2NH3)

Answer 17

No. The reactants of ammonia synthesis have very high bond energies making them unreactive. A catalyst is required such as iron to drive the reaction to equilibrium.

Question 18

In a Pepsi bottle, what happens if you open it?

Answer 18

There is a decrease in pressure so the reaction shifts and a new equilibrium is established

Question 19

In a Pepsi bottle, where do the bubbles come from? How is it dynamic?

Answer 19

Carbonic acid decomposing into CO2 and water. Both forward reactions and reverse occur at same time (synthesizing H2CO3 and decomposition)