Acids, pH and equilibrium Flashcards Preview

A2 Chemistry (Unit 2: F325) > Acids, pH and equilibrium > Flashcards

Flashcards in Acids, pH and equilibrium Deck (36)
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1

What is the equilibrium law?

For the equilibrium:aA + bB ⇔ cC + dD,Kc (Equilibrium constant) = ([C]c x [D]d)/([A]a x [B]b). 

2

What is a homogeneous equilibrium?

An equilibrium in which all the species making uop the reactants and products are in the same phase.

3

What is a heterogeneous equilibrium?

An equilibrium in which species making up the reactants and products are in different phases.

4

What is the significance of the Kc value?

1. A Kc value of one exactly indicates the position of equilibrium being in the middle.2. A Kc value of < 1 indicates the position of equilibrium is in favour of the reactants.3. A Kc value of > 1 indicates the position of equilibrium is in favour of the products. 

5

What effect on the Kc value does changing the temperature have?

- Increasing the temperature of an exothermic shifts the position of equilibrium to the left, in favour of the endothermic reverse reaction, decreasing value of Kc.- Increasing the temperature of an endothermic reaction shifts position of equilibrium to the right, in favour of the endothermic forward reaction, increasing value of Kc.

6

What effect on the Kc value does changing the pressure/concentration have?

Changing the pressure/concentration doesn't affect the value of Kc. However, it does change the concentration of reactants and products, which would change the Kc value, thus position of equilibrium shifts to maintain a constant Kc value.

7

What effect on the Kc value does adding a catalyst have?

Value of Kc is unaffected by the addition of a catalyst.

8

What is k (rate constant)?

Constant determining the rate of a reaction under specific conditions.

9

What is the relationship between k and Kc during a compromise?

During a compromise, a big value of Kc results in a small value of k, and vice versa. This means that a balance needs to be struck so that a big enough k value is obtained so that the reaction isn't too slowwithout compromising decreasing the value of Kc too much so that a low yield is obtained.

10

What is a Brønsted-Lowry acid?

A proton, H+, donor.

11

What is a Brønsted-Lowry base?

A proton, H+, acceptor.

12

What is an alkali?

A water soluble base that releases hydroxide (OH-) ions when in solution.

13

What is a neutralisation reaction?

A chemical reaction in which an acid and a base react together to produce a salt and water.

14

What is a monobasic acid?

An acid whereby each molecule is able to release up to one proton each. E.g. HCL.

15

What is a dibasic acid?

An acid whereby each molecule is able to release up to two protons each. E.g. H2SO4.

16

What is a tribasic acid?

An acid whereby each molecule is able to release up to three protons each. E.g. H3PO4.

17

Why is H2SO4 acidic when dissolved in H2O but not when liquid?

For a compound like H2SO4 to be acidic, it needs to release protons (dissociate). However, it would only release a proton if there is another compound present to accept the proton (a base). In water, water molecules act as bases and accept protons from acid:H2SO4 + H2O → HSO4- + H3O+As liquid, no molecules are able to act as bases, so H2SO4 is not acidic.

18

What is a conjugate acid?

A species formed when a proton is added to a base.

19

What is a conjugate base?

A species formed when a proton is removed from an acid.

20

What is an acid-base pair?

A pair of two species that transform into each other by the gain or loss of a proton. 

21

What is an example of acid-base pairs?

HCl + H2O → H3O+ + Cl-In this equation: HCl is the acid, Cl- is its conjugate base (since Cl- becomes HCl by gaining proton).H2O is the base, H3O+ is the acid (since H3O+ becomes H2O by losing proton).

22

What is the formula of pH?

pH = -log10[H+(aq)]

23

What is a strong acid?

An acid that completely dissociates in solution.

24

What is a weak acid?

An acid that partially dissociates in solution.

25

What is the ionic product of water (Kw)?

Kw = [H+(aq)][OH-(aq)]at 298K, Kw = 1 x 10-14 mol2dm-6.

26

What is significant about Kw?

At a given temperature, Kw is constant no matter the pH of the solution in question.

27

What is the only factor that changes Kw?

Temperature.

28

What is the acid dissociation constant (Ka)?

The actual extent to which an acid dissociates in solution. The Ka of an acid HA is defined as:Ka = [H+(aq)][A-(aq)]/[HA(aq)]

29

What is the significance of the Ka value?

A large Ka value means that the acid dissociates readily and thus is a stronger acid.A small Ka value means that the acid dissociates less and thus is a weaker acid.

30

What is a buffer solution?

A mixture that minimises pH change on addition of small amounts of acid or base.