5B -equilibria

Question 1

Define dynamic equilibrium

Answer 1

A state of an equilibrium in a closed system such that the rate of the forwards reaction is the same as
the reverse and the concentrations of reactants and products do not change.

Question 2

define closed system

Answer 2

A systme isolated from the surroundings where no molecules are able to exit or enter

Question 3

How can you use the value of Kc or Kp to estimate the position of equilibrium? Hint: use the
general equation.

Answer 3

As the general equation for the equilibrium constants is products over reactants, if the value of Kc or
Kp is greater than 1 then the concentration or partial pressures of products is greater than that of the
reactants so position of equilibrium will be to the right.
If Kc is less than 1 then the partial pressure of the reactants is greater than that of the products so the equilibrium shifts to the left

Question 4

define Le Chatelier’s principle

Answer 4

When a system in dynamic equilibrium is subjected to an external change, the system readjusts itslef to minimse the effect of the cahgne and to restore equilibrium

Question 5

How do you calculate a mole fraction?

Answer 5

Mole fraction = Moles of given gas ÷ Total moles

Question 6

How do you calculate partial pressure?

Answer 6

Partial Pressure(A) = Mole fraction x Total Pressure

Question 7

Write the general equations for Kc

Answer 7

𝐾𝑐 =

[𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑠] / [𝑅𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]

Question 8

Write the general equations for Kp

Answer 8

𝐾𝑝 =

𝑝(𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑠) / 𝑝(𝑅𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠)

Question 9

Explain the impact on Kc/Kp by changing the temperature

Answer 9

1.The reaction is endothermic / exothermic in the forwards direction.
2. Therefore when the reaction mixture is heated / cooled, the position of
equilibrium will shift to the left / right.
3. The numerator increases / decreases and the denominator
decreases / increases,
4. so Kc/Kp increases / decreases as a result

Question 10

Adding or removing a reactant or product

Answer 10

1. Initially, the numerator / denominator increases / decreases.
2. Since Kc / Kp is constant at a fixed temperature,
3. to re-establish equilibrium, the numerator / denominator must
   increase / decrease, and as a consequence, the denominator / numerator
   must decrease / increase.
4. This is a shift in position of equilibrium to the left / right.

Question 11

Changing the total pressure or volume

Answer 11

1. Initially, all the concentrations / partial pressures increases / decreases.
2. As the numerator is raised to a higher / lower total power than the
   denominator,
3. the numerator increases / decreases more / less than the denominator.
4. Since Kc / Kp is constant at a fixed temperature,
5. to re-establish equilibrium, the numerator must increase / decrease
   and the denominator decrease / increase.
6. This is a shift in position of equilibrium to the left / right.