Equilibrium

Question 1

What is the thing that affects Kc? What is the relationship?

Answer 1

Temperature affects Kc. It causes the position of equilibrium to shift to oppose the change. Dictated by the enthalpy of the forward reaction. If exothermic and temperature increased, Kc moves to other side to absorb energy and decrease overall change.

Question 2

What is the difference between SN1 and SN2 mechanisms?

Answer 2

SN1 has one molecular - it is the monomolecular reaction mechanism. One molecule in the rate determining step.

SN2 is a bimolecular mechanism. Two molecules are involved in the rate determining step.

Question 3

What are the conditions required for a dynamic equilibrium?

Answer 3

Closed system in which forward and reverse reaction rates are equal and the concentrations of reactants and products are constant.

Question 4

What is the difference between Le Chatelier and the equilibrium law?

Answer 4

The equilibrium law actually works. All the fucking time, unlike Le Chat, which is a principal, so it doesn’t.

Question 5

What is the colour of NO2 and N2O4

Answer 5

NO2 - brown

N2O4 - colourless

Question 6

What is the calculation for reacted moles?

Answer 6

Initial moles - equilibrium moles

Question 7

What is the definition of equilibrium moles?

Answer 7

The moles left when a system has reached equilibrium.

Question 8

What does it mean if Kc has no units?

Answer 8

There are the same number of moles on each side, hence they cancel. This means we don’t need to know the volume, as it cancels from the equation. Just sub in V to show calculation of concentration, not moles.

Question 9

Define equilibrium moles

Answer 9

The amount of reactant or product left when the reaction has reached equilibrium. The concentrations of these are constant.

Question 10

What colour is N2O4

Answer 10

Brown

Question 11

What colour is NO2 gas

Answer 11

colourless

Question 12

Define homogeneous equilibria

Answer 12

An equilibrium where all the reactants and products are in the same states

Question 13

What measurement do we use to calculate Kc?

Answer 13

Equilibrium concentrations.

Question 14

Once we have reacted moles of one product or reactant, what can we use to find the rest?

Answer 14

Stoichiometric relationship

Question 15

What does a large value of Kc suggest about the position of equilibrium?

Answer 15

Lies to the RHS. Product concentration larger than reactant concentration

Question 16

What does a small value of Kc suggest about the position of equilibrium?

Answer 16

It lies to the LHS. Reactant concentration larger than product concentration

Question 17

To which side of a reaction does an increase in temperature cause the shift?

Answer 17

endothermic side, to absorb increase in temperature

Question 18

To which side of a reaction does a decrease in temperature cause the shift?

Answer 18

Exothermic side, to release more energy

Question 19

What happens when concentration of reactant is increased, but not the product?

Answer 19

The system is momentarily not in equilibrium. Kc has changed, and the concentrations of products and reactants must adjust to return Kc to its original value. This means the system favours the products, increasing their concentration, whilst decreasing concentration of reactants. Kc then returns to its starting value and the system is in equilibrium.

Question 20

Which species do we remove from the equation for Kstab and why?

Answer 20

Displaced water molecules are left out in ligand substitution as all solutions are aqueous, so the concentration of water is virtually constant.

Question 21

Define the stability constant Kstab

Answer 21

It is the equilibrium constant relating a transition metal surrounded by water molecules and the complex after undergoing ligand substitution. It tells us the stability of the transition metal complex formed.

Question 22

If the concentration of one reactant increases, what do we know about the changes in equilibrium amounts of the other reactants and products. Use the example of H2 + I2 –> 2HI

Answer 22

If the reactant that is in excess is increases, the equilibrium amount stays the same as the other reactant is limiting.

If the limiting reagent is increased, the equilibrium amount increases. This means the value of Kc is no longer in equilibrium. To counter this, the other reactant decreases in concentration, and the products increase in concentration

Question 23

If the pressure of a system is increased, what would happen to the value of Kc?

Answer 23

It would stay the same as KC is independent of pressure, and is only dependent on temperature.

Question 24

When the pressure of the ammonia equilibrium is increased, what happens to the yield of NH3 and why?

Answer 24

If the pressure is increased, the system is no longer in equilibrium. The concentrations on the bottom of the expression increase more than NH3 on the top due to the powers (orders). In order to return to equilibrium, the moles on the bottom must decrease, and the moles on the top must increase to return Kc to its original value

Question 25

What do you have to check when you’re finding Kc from equilibrium moles

Answer 25

Convert from moles to concentration by dividing by volume.

YOU WILL BE LUCKY TO GET SAME MOLES ON TOP AND BOTTOM.