Equilibria

Question 1

In the following equation, which is the larger contributed to global warming?

CO₂ (g) ⇔ CO₂ (aq)

Answer 1

CO₂ (aq)

Question 2

draw a graph to represent the following equations and the species concentration over time?

Explain why the graph is the shape you’ve drawn it

Answer 2

As the graph plateaus, at this point the slopes of both lines become flat (horizontal) telling us that the concentration of both A + B and C + D are no longer changing. The reactions are now at equilibrium

Question 3

Whats a system is dynamic equilibrium?

Draw a graph to explain this?

Answer 3

The rates of the forward and backward reactions are equal.

There is no overall change in the system, eben though both reactions continue to occur

Question 4

If the rates of the forward and backwards reactions are the same. Does this mean that the concentrations are the same?

Answer 4

No, the concentrations could be different but the ratio between the two always remains the same

Question 5

Whats the formula for the equilibrium constant ?

What does each part represent?

Answer 5

Kc= products/ reactants

Question 6

What are the 2 things that you must remember about the Kc constant?

Answer 6

• The value of Kc is dimensionless as the units cancel each other out
• the units for the concentration are always in units of mol/L (M not mmol/L etc.)

Question 7

What state cannot be used in the Kc equation?

Answer 7

(s)

Question 8

Whats the eqaution for the partial pressure of a gas?

What does each part represent?

Answer 8

P_{A =} X_A x p

P_A= partial pressure of gas ‘A’

X_A= Mole fraction of gas ‘A’

p= total pressure of the system

Question 9

Whats the equation for the mole fraction?

Answer 9

X_A= numbr of moles of substance A / Total number of moles of all substances

Question 10

What must X_A be less than?

Answer 10

1

Question 11

Whats the formula for K_P?

Answer 11

Question 12

When is Kc small/ large?

Answer 12

Question 13

Tell me about the reaction quotient

whats its formula?

Answer 13

Question 14

What are the factors that change the reaction at equilibrium?

Answer 14

1. concentration
2. temperature
3. pressure

Question 15

Whats La Châteliers principle?

Answer 15

When a chemical system at equilibrium is disturbed, it responds by shifting the equilibrium composition in such a way to counteract the change

Question 16

How does a catalyst effect the equilibrium?

Answer 16

A catalyst is a substance that speeds up a chemical reaction without being consumed. It increases both the forward and backward reactions to the same extent

A catalyst DOES NOT change the equilibrium constant, it remains unchanged

Question 17

Whats Arrhenius definition of an acid and a base?

Answer 17

Acid: increases the concentration of H₃O⁺ ions in solution

Base: increases the concentration of OH- ions in solution

Question 18

How does an acid work…

Answer 18

An acid can work either by donating a proton, H+, to the solution or by removing OH- from a water molecules

HCl (aq) ⇔ H+ (aq) + Cl- (aq) [HCl ⇒ H⁺ + Cl-]

Question 19

How does a base work…

Answer 19

Similarly, a base can work either by donating OH- to the solution, or by removing a proton from a water molecule

NH3 (aq) + H2O ⇔ NH4⁺ (aq) + OH- (aq)

Question 20

Whats the definition of acids and bases, based on?

Answer 20

The definition of acids and bases is based on the equilibrium for ionic dissociation for water- it is a thermodynamic definition

Question 21

For pure water at 298K, [H₃O⁺] = 10^-7 and so pH= 7.0

How is acids and bases defined under these conditions?

Answer 21

Acidic solution [H₃O⁺] > 10^-7 M PH<7

Basic solution [H₃O⁺] < 10^-7 M PH>7

the pH range for most experiments is from 0 (1M of H₃O⁺ ions)

to 14 (1M of OH- ions in solution)

Question 22

Label the conjugate acid and bases in the following equations…

Answer 22

Question 23

What are buffers?

Answer 23

When the concentrations of the conjugate acid and base are approximately equal

Question 24

Whats the acid dissociations formula?

Answer 24

Question 25

Whats the relationship equations between pH and PK_a?

Answer 25

PK_a= -log₁₀ K_a

K_a= 10^-Pk_a

Question 26

In acid dissociation equations, water isn’t ever included. Why is this and what formula explains why?

Answer 26

As water is constant and very large (55.5M), its not included in the Ka equation, it can be removed by multiplying both sides by [H2O]

Question 27

Tell me the size of the K_a for strong and weak acids

Answer 27

A strong acid has a large K_a

A weak acid has a small K_a

Question 28

Whats the equation for the ionic product of water?

Answer 28

K_w = [H⁺] [OH^-]