3.2

Question 1

what is standard enthalpy change of formation?

Answer 1

The enthalpy change when one mole of a compound is formed from its elements in their standard states.

Question 2

what is enthalpy change of combustion?

Answer 2

The enthalpy change for the complete combustion of one mole of a substance.

Question 3

what is enthalpy change of neutralisation?

Answer 3

the enthalpy change for the formation of 1 mol of water from neutralisation.

Question 4

what is activation energy?

Answer 4

the minimum energy required for a reaction to take place.

Question 5

what is a homogenous catalyst?

Answer 5

A catalyst in the same state as the reactants.

Question 6

what is a heterogenous catalyst?

Answer 6

• A catalyst in a different state to the reactants.

Question 7

what is dynamic equilibrium?

Answer 7

When the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products do not change in a closed system.

Question 8

Why is experimental value different from ΔHc values?

Answer 8

1) not standard conditions
2) heat lost to surroundings
3) incomplete combustion

Question 9

Why can’t you measure enthalpy changes directly ?

Answer 9

1) Ea too high
2) other products may form
3) (reaction happens too slowly/ not at all )

Question 10

how do you experimentally find enthalpy change of combustion?

Answer 10

1) weigh fuel
2) measure volume of water
3) burn fuel in a spirit burner to heat water
4) measure temperature change using thermometer
5) reweigh fuel
6) use q=mcΔT and ΔH=-q/n

Question 11

what is the setup for the experiment measuring enthalpy change of combustion and improvements?

Answer 11

beaker on a clamp stand-improvement: use calorimetry cup with lid, use insulating jacket
water in beaker- if asked 50g or 100g
spirit burner containing fuel being tested

Question 12

how do you measure enthalpy change of neutralisation?

Answer 12

1) measure out acid+ alkali of known concentration
2) measure temp change
3) use q=mcΔT for total volume and ΔH=-q/n. use n=cxv for limiting agent.

Question 13

how do you measure enthalpy change of reaction?

Answer 13

1) add 50cm3 solution1/acid to cup
2) record temp of solution
3) add zinc and start timer. stir with thermometer
4) record temperature at regular intervals
5) plot graph and extrapolate
6) find ΔT. use q=mcΔt and -q/n.

Question 14

WHAT DO YOU NEED TO REMEMBER ABOUT THE BOLTZMANN

Answer 14

IT DOESN’T CROSS THE X AXIS AT THE HIGH ENERGY

Question 15

why does the use of a catalyst reduce energy demand?

Answer 15

less HEAT/THERMAL energy is required for the reaction. less FOSSIL FUELS are burnt leading to less CO2 emissions.

Question 16

in q=mcΔt, what should you use the moles of and what should you use the volume of?

Answer 16

moles of solid (unless the solid’s specifically in excess)

volume of liquid

Question 17

how does decreasing pressure affect rate of reaction?

Answer 17

less particles per unit volume

less frequent collisions.

Question 18

how can gases react with a solid catalyst?

Answer 18

1) adsorption of gases- gases attach to surface
2) bonds weaken in reactants-bonds break-new bonds form in products-activation energy decreases
3) desorption of products-released from surface

Question 19

why is it not possible to measure enthalpy change directly?

Answer 19

• reaction gives mixture of products
• Ea too high
• rate of reaction too slow
• reactants don’t react

Question 20

what is activation energy

Answer 20

the MINIMUM energy needed for reactants to react.

Question 21

what is enthalpy change of reaction?

Answer 21

when the number of moles of reactants as specified in the equation react together.

Question 22

what is bond enthalpy?

Answer 22

enthalpy change when 1 mole of gaseous covalent bonds are broken.

Question 23

how can energy be used to lower the cost of a certain reaction?

Answer 23

used to heat reactants
used to heat rest of factory
sold to national grid

Question 24

why shouldn’t you use a low temperature if it shifts equilibrium to the products?

Answer 24

rate of reaction would be too slow.

Question 25

energy is …. to break bonds

Answer 25

required

Question 26

energy is… making bonds

Answer 26

released

Question 27

WHY MIGHT STANDARD ENTHALPY CHANGE OF COMBUSTION BE DIFFERENT TO CALCULATED VALUES FROM AVERAGE BOND ENTHALPIES?

Answer 27

actual bond enthalpies may be different from average values

conditions are not standard.

Question 28

WHAT STATE IS BUTANE (C4H10?)

Answer 28

GAS

Question 29

WHAT IS ENTHALPY CHANGE OF HYDRATION

Answer 29

ENTHALPY CHANGE WHEN 1 MOLE OF GASEOUS IONS FULLY DISSOLVE IN WATER.

Question 30

WHAT IS AVERAGE BOND ENTHALPY

Answer 30

ENTHALPY CHANGE WHEN 1 MOLE OF BONDS IN GASEOUS MOLECULES ARE BROKEN. HAVE TO SAY MOLECULES, DONT SPECIFY THE TYPE OF BOND.