physical chemistry

Question 1

definition of chemical equilibrium

Answer 1

when composition of the reactants and products remains constant indefinitely

Question 2

what does the value of K indicate?

Answer 2

position of equilibrium

Question 3

what is given a value of 1 at equilibrium?

Answer 3

concentrations of pure solids and pure liquids (water)

Question 4

what is the one factor which affects K value?

Answer 4

temperature

Question 5

effect of increasing temperature on K value

Answer 5

exothermic reactions - decrease in K
endothermic reactions - increase in K

Question 6

meaning of different K values (>/<1)

Answer 6

> 1 = equilibrium lies to right
<1 = equilibrium lies to left

Question 7

effects of a catalyst on equilibrium

Answer 7

• no effect on position
• increases rate of forward and reverse reactions equally
• no change to K value
• equilibrium reached more quickly

Question 8

dissociation of strong acids

Answer 8

dissociates fully into its ions, equilibrium lies almost fully to the right

Question 9

dissociation of weak acids

Answer 9

dissociates partially into its ions, equilibrium lies almost fully to the left

Question 10

examples of strong acids

Answer 10

hydrochloric, sulfuric, nitric

Question 11

examples of weak acids

Answer 11

carboxylic, sulphurous, carbonic

Question 12

examples of strong bases

Answer 12

group 1&2 metal hydroxides (except magnesium)

Question 13

examples of weak bases

Answer 13

ammonia, ammines

Question 14

Bronstead & Lowry definitions of acids and bases

Answer 14

acids donate protons, bases accept protons

Question 15

what’s a conjugate base?

Answer 15

substance left over when an acid donates a proton (what acid becomes)

Question 16

what’s a conjugate acid?

Answer 16

substance made when a base accepts a proton (what base becomes)

Question 17

what does amphoteric mean?

Answer 17

acts as both an acid and a base e.g water

Question 18

what is a buffer solution?

Answer 18

solution where the pH will remain approximately constant when a small amount of acid, alkali or water is added.
often used to calibrate pH meters.

Question 19

what are acidic buffers made of?

Answer 19

a weak acid and the salt of that acid

Question 20

what are basic buffers made of?

Answer 20

a weak base and the salt of that base

Question 21

what are indicators?

Answer 21

weak acids which change colour depending on the pH of the solution

Question 22

why does the colour change in the presence of an indicator?

Answer 22

equilibrium shifts

Question 23

selecting indicator based on acid/base combo

Answer 23

both strong: indicator must change colour around pH 7
strong acid/weak base: indicator must change colour around pH 5
weak acid/strong base: indicator must change colour around pH 9

Question 24

enthalpy definition

Answer 24

energy stored in chemical bonds

Question 25

enthalpy of formation definition

Answer 25

enthalpy change when one mole of a substance is prepared from its constituent elements in their standard states.

Question 26

entropy definition

Answer 26

the measure of the disorder in a system

Question 27

states and entropy

Answer 27

gaseous substances have greater entropy than liquid ones, liquid substances have greater entropy than solid ones

Question 28

ways to increase entropy

Answer 28

• increase temperature
• break a large molecule down into smaller ones

Question 29

how to calculate entropy

Answer 29

take away entropy of reactants from that of the products

Question 30

what does negative entropy mean?

Answer 30

decreased entropy = reaction becoming more ordered

Question 31

relationship between enthalpy and entropy

Answer 31

if enthalpy is positive, so is entropy, and vice versa

Question 32

first law of thermodynamics

Answer 32

energy cannot be created or destroyed, only changed from one form to another

Question 33

second law of thermodynamics

Answer 33

the total entropy of a reaction system and its surroundings always increases for a spontaneous reaction

Question 34

third law of thermodynamics

Answer 34

the entropy of a perfect crystal at 0K is zero as particles have no kinetic energy.

Question 35

exo/endo and entropy

Answer 35

exothermic reactions increase the entropy of the surroundings.
endothermic reactions decrease the entropy of the surroundings

Question 36

Gibbs free energy for spontaneous reactions

Answer 36

Gibbs energy must be negative for a reaction to be spontaneous (feasible)

Question 37

feasible reactions?

Answer 37

tend towards products rather than reactants

Question 38

Gibbs energy at equilibrium?

Answer 38

• zero
• a reaction will proceed spontaneously until the conformation is reached where ^G=0

Question 39

entropy changes and feasibility

Answer 39

if entropy change is negative, then anything below T is feasible.
if entropy change is positive, anything above T is feasible.

Question 40

what does first order mean?

Answer 40

when concentration of reactant doubles, so does rate of reaction

Question 41

what does second order mean?

Answer 41

when concentration doubles, rate of reaction quadruples.

Question 42

what does 0 order mean?

Answer 42

changing concentration of reactant has no effect on rate of reaction

Question 43

how to find overall order

Answer 43

add orders of each reactant together

Question 44

what is rate determining step?

Answer 44

slower step in reaction mechanism