module 3.2

Question 1

what is activation energy

Answer 1

the minimum emery particles need for collisions to be successful and result in reaction

Question 2

what are standard conditions

Answer 2

298K and 1atm solutions at 1M

Question 3

what is the enthalpy change of reaction

Answer 3

the enthalpy change for a given reaction

Question 4

what is the enthalpy change of formation

Answer 4

the enthalpy change when forming 1 mol of a compound from its elements in their standard states

Question 5

what is the enthalpy change of combustion

Answer 5

enthalpy change for the complete combustion of 1 mol of a substance

Question 6

what is the enthalpy change of neutralisation

Answer 6

the enthalpy change for the formation of 1 mol of water from a neutralisation reaction

Question 7

what is the average bond enthalpy

Answer 7

the enthalpy change for breaking 1 mol of bonds in gaseous molecules

Question 8

what is hess’ law

Answer 8

the enthalpy change of a reaction is independent of the route taken

Question 9

what do the arrows in hess cycles mean

Answer 9

up is making bonds down is breaking bonds (goes towards it if it’s being made or away if it’s breaking up)

Question 10

what is chemical energy

Answer 10

the potential energy stored in bonds

Question 11

what is enthalpy

Answer 11

chemical energy

Question 12

what concentration should every solution be in enthalpy calculations

Answer 12

1mol dm^-3

Question 13

values of enthalpy change of formation

Answer 13

usually but not exclusively exothermic

Question 14

values of enthalpy change of combustion

Answer 14

always exothermic

Question 15

values of enthalpy of neutralisation

Answer 15

always exothermic

Question 16

what is the enthalpy change of neutralisation strong acids and strong alkalais

Answer 16

-57 kJ mol^-1

Question 17

what’s enthalpy change unit

Answer 17

kJ mol^-1

Question 18

what’s the calorimetery equation and what does each letter stand for with units

Answer 18

q=mc@T
q= heat energy J
m= mass g
c= specific heat capacity J g^-1 K^-1
@T= temperature change K (but change in °C is the same)

Question 19

what is specific heat capacity

Answer 19

the energy required to raise the temperature of 1g of a substance by 1K

Question 20

how do you determine enthalpy change from calorimetry equation

Answer 20

work out q, put in kJ, then divide by the moles (because enthalpy change is the energy needed for one mole)

Question 21

what’s the enthalpy of formation for elements in their standard state

Answer 21

0

Question 22

where will the enthalpy change of neutralisation arrow point

Answer 22

towards the water

Question 23

how do you deal with O2 and CO2 in enthalpy cajnge of combustion

Answer 23

ignore it because they’re products and would cancel out

Question 24

what is collision theory

Answer 24

for a reaction to happen particles must collide with enough energy (activation energy) for the collisions to be successful

Question 25

what are the five factors that affect rate of reaction

Answer 25

temperature pressure catalyst concentration surface area

Question 26

why do catalysts increase rate of reaction

Answer 26

they lower activation energy by providing an alternate pathway so a greater proportion of particle collisions that have the activation energy so more frequent successful collisions

Question 27

what is a heterogeneous catalyst

Answer 27

catalyst is in a different phase (state) to the reactants

Question 28

what is a homogeneous catalyst

Answer 28

catalyst is in the same phase (state) as the reactants

Question 29

how does a heterogeneous catalyst work

Answer 29

reactants ADSORPED to the active site on the surface of the catalyst, they form weak bonds with metal atoms whcih uses some bonding electrons thus weakening the bonds. REACTION takes place which requires less energy. DESORPTION is the last step when the products are released

Question 30

what is catalyst poisoning

Answer 30

when the surface of a catalyst is coated in a substance that cant desorb thus removing potential active sites and decreasing efficiency

Question 31

what is dynamic equilibrium in a closed system

Answer 31

when the rate of reaction is the same in both directions of a reversible reaction, meaning the concentrations of the reactants and products don’t change

Question 32

what is le chateliers principle

Answer 32

if equilibrium is disturbed by changing the conditions the position of equilibrium shifts to counteract the change to re-establish an equilibrium

Question 33

what condition permanently affects equilibrium constants and why

Answer 33

temperature change because it affects the energy in the reaction rather than the chemicals (which can be rectified)

Question 34

how would: aA + bB <=> cC + dD be put in an equation to work out Kc

Answer 34

[C]^c [D]^d —————- = Kc (constant) [A]^a [B]^b

Question 35

what are the rules when constructing an equilibrium constant equation

Answer 35

square brackets around the equilibrium concentration in mol dm^-3 raised to the power of the stoichiometry number with reactants over products

Question 36

how do you work out the units of equilibrium constants

Answer 36

use the powers from the stoichiometry numbers and use indice laws from the base mol dm^-3

Question 37

where is equilibrium if Kc= 1

Answer 37

halfway between the reactants and products

Question 38

what happens to equilibrium if K<1 (smaller than 1)

Answer 38

equilibrium is to the left, favouring reactants

Question 39

what happens if K>1 (bigger than 1)

Answer 39

equilibrium is to the right, favouring products

Question 40

what word should you use when discussing changing concentration on Kc values

Answer 40

restores Kc to x

Question 41

how do you set up calculations for Kc

Answer 41

create balanced equation with state symbols Initial Change Equilibrium (in mol) use c=n/V (remember mol dm^-3) if no volume stated use V it should cancel out later sub into usual equation

Question 42

what is X in [X] in Kc calculations

Answer 42

the equilibrium concentration

Question 43

what are the axis on a boltzmann distribution

Answer 43

x = energy y = number of molecules with a given energy

Question 44

what does the area under a boltzmann curve represent

Answer 44

total number of molecules in the sample

Question 45

what must you rememebr when drawing a boltzmann

Answer 45

must begin at the origin once it starts coming down it never goes up again never touches the x axis after the origin

Question 46

how does a boltzmann curve change with increased temperature

Answer 46

flattens and broadens, shifts to the right

Question 47

how does a catalyst affect a boltzmann graph

Answer 47

curve stays the same, the activation energy just shifts left

Question 48

what direction should an arrow in a hess cycle representing bond enthalpy point?

Answer 48

down away from the molecule

Question 49

how does a bigger surface area increase rate of reaction

Answer 49

more sites for reactions

Question 50

what is a catalyst

Answer 50

a substance that increases the rate of a reaction without being used up in the process

Question 51

how is a catalyst shown in an energy profile diagram

Answer 51

a lower activation energy peak

Question 52

how does a boltzmann curve change with reduced temperature

Answer 52

narrower higher peak to the left

Question 53

what will happen to equilibrium if you increase the temp?

Answer 53

shifts to favour the endothermic reaction

Question 54

what will happen to equilibrium if you increase the pressure?

Answer 54

shifts to favour the reaction with less GASEOUS moles

Question 55

what will happen to equilibrium if you increase the concentration of the reactants?

Answer 55

will shift to the right to make more product

Question 56

what’s the affect of a catalyst on the position of equilibrium?

Answer 56

no affect because it only affects the activation energy

Question 57

why might enthalpy changes of combustion be less exothermic than expected when determining experimentally? (two reasons)

Answer 57

it is difficult to stop heat escaping, can get absorbed by equipment theoretical values assume complete combustion which is difficult to achieve