Chemical Equilibrium

Question 1

reaction is in chemical equilibrium when

Answer 1

the rate of the forward reaction equals the rate of the reverse reaction

Question 2

4 requirements for chemical equilibrium to be reached

Answer 2

Rate forward = Rate reverse.
Closed System: no reactants or products lost.
all appears constant (no VISIBLE changes)
DYNAMIC (moving)- changing on ATOMIC level

Question 3

equilibrium constant

Answer 3

Kc
constant which represents how far the reaction will proceed at a given temperature

Question 4

Kc greater than 1

Answer 4

products exceed reactants (at
equilibrium)
When much greater than 1, the reaction goes almost to completion

Question 5

Kc less than 1

Answer 5

reactants exceed products
When much less than 1 (Kc can never be negative, when it is close to zero) the reaction hardly occurs at all

Question 6

only thing which can change the value of Kc for a given reaction

Answer 6

change in temperature
position of equilibrium, however, can change without a change in the value of Kc

Question 7

The Haber Process

Answer 7

combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia
reaction is reversible
production of ammonia is exothermic

Question 8

Haber Process conditions

Answer 8

400-450 degrees
200 atm
iron catalyst (with potassium hydroxide, increases efficiency)
N2:H2 = 1:3
Recycling, only about 15% of the nitrogen and hydrogen converts to ammonia
overall conversion is about 98%

Question 9

Le Chatelier’s principle

Answer 9

The principle that if a system in chemical equilibrium is subjected to a disturbance it tends to change in a way that opposes this disturbance

Question 10

Le Chatelier’s principle: Changes in Conc

Answer 10

adding additional reactants to a system will shift the equilibrium to the right, towards the side of the products.
By the same logic, reducing the concentration of any product will also shift equilibrium to the right.
reversible reactions are self-correcting

Question 11

Le Chatelier’s principle: Changes in Pressure

Answer 11

pressure in a system increases, or the volume decreases, the equilibrium will shift to favour the side of the reaction that involves fewer moles of gas.
increase pressure by decreasing volume, the equilibrium would shift to the right, counteracting the pressure increase by shifting to the side with fewer moles of gas that exert less pressure

Question 12

Le Chatelier’s principle: Changes in Temp

Answer 12

raise the temperature on an endothermic reaction, it is essentially like adding more reactant to the system, and therefore, by Le Chatelier’s principle, the equilibrium will shift to the right.
exothermic reaction, heat is a product. Therefore, increasing the temperature will shift the equilibrium to the left, while decreasing the temperature will shift the equilibrium to the right.
catalyst does not affect either Kc or the position of equilibrium, only the rate of reaction