Mod 5 topic 3

Question 1

What is the Equilibrium constant

Answer 1

a mathematical relationship to show concn of reactant and products

Question 2

Eqlm expression for aA + bB <–> cC + dD

Answer 2

Keq = [C]^c x [D]^d/[A]^a x [B]^b

Question 3

Why are solutions and gases always included in Keq

Answer 3

Solutions and gases vary in concentration and are thus always included.

Question 4

What is not included in heterogenous systems (different phases present) Keq

Answer 4

Solids and liquids are NOT included

Question 5

Is everything included in a homogenous system (same phase)

Answer 5

No, Pure solids and pure liquids are not included in 𝐾𝑒𝑞 because their activities are constant.

Question 6

If Keq = ~1:

Answer 6

Then the concentration of reactants and products is approximately equal at equilibrium.

Question 7

If Keq < 1

Answer 7

There are more reactants (bottom of fraction is larger) and the equilibrium lies to the left.

Question 8

If Keq > 1

Answer 8

there are more products (top of fraction is larger) and the equilibrium lies to the right.

Question 9

What must all concn values be for Keq questions

Answer 9

All concentration values must be in mol L-1 – if concentration is given in other units it must be converted prior to substitution.

Question 10

What is the effect of temperature on Keq?

Answer 10

Keq is specific to a particular temperature and changes when temperature changes.

Question 11

Does Keq change when concentration, pressure, or other factors change?

Answer 11

No, bc Keq is at eqlm, not directly after a change, it stays the same; the system shifts by Le Chatelier’s principle to restore the original ratio.

Question 12

Why does Keq not change when concentration changes?

Answer 12

Changing concentration means Q ≠ Keq, and the system (by LCP) shifts to restore Keq.

Question 13

Why does Keq change when temperature changes?

Answer 13

Temperature alters RR(forward) and RR(reverse), thus changing the final product/reactant ratio, so Keq is different from the initial value.

Question 14

For the exothermic reaction Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺, what happens when temperature increases?

Answer 14

The system shifts in the endothermic (reverse) direction. The reverse reaction is favoured because the forward reaction is exothermic.

Question 15

How does increasing temperature affect concentrations in the exothermic reaction Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺ reaction?

Answer 15

Reactant concentrations increase and product concentration decreases.

Question 16

What is the equilibrium constant for dissociation of ionic solids called?

Answer 16

The solubility product, Ksp.

Question 17

What does a small Ksp indicate?

Answer 17

The substance produces few ions and is poorly soluble.

Question 17

What does ionic product = Ksp mean?

Answer 17

The system is at equilibrium.

Question 18

What does a large Ksp indicate?

Answer 18

The substance produces many ions and is highly soluble.

Question 19

What is the equivalent of Q for ionic equilibria?

Answer 19

The ionic product.

Question 20

What does ionic product > Ksp mean?

Answer 20

Reverse reaction is favoured and more precipitate forms.

Question 21

What does ionic product < Ksp mean?

Answer 21

Forward reaction is favoured and more ions form.

Question 22

What is Q and what does it represent

Answer 22

The reaction quotient. It is calculated the same way as Keq, but is used to show you dont know whether the reaction is at eqlm

Question 23

What does it mean if Q = Keq,

Answer 23

The system is at eqlm

Question 24

What does it mean if Q < Keq,

Answer 24

Denom is larger, meaning there are more reactants and less products than at eqlm. Thus eqlm needs to shift to the right to increase the products (numerator) and increase the Q value to match Keq

Question 24

What does it mean if Q > Keq,

Answer 24

Numerator is larger, meaning there are more products and less reactants than at eqlm. Thus eqlm needs to shift to the left to increase the reactants (denominator) and decrease the Q value to match Keq