Energetics

Question 1

bond breaking is (exothermic/endothermic)

Answer 1

endothermic

Question 2

bond forming is (exothermic/endothermic)

Answer 2

exothermic

Question 3

Endothermic reactions (release/absorb) energy

Answer 3

absorb

Question 4

Exothermic reactions (release/absorb) energy

Answer 4

release

Question 5

Endothermic reactions are (cold/hot)

Answer 5

cold

Question 6

Exothermic reactions are (cold/hot)

Answer 6

hot

Question 7

Endothermic reactions have a (positive/negative) delta H

Answer 7

positive

Question 8

Exothermic reactions have a (positive/negative) delta H

Answer 8

negative

Question 9

Temperature

Answer 9

average kinetic energy of a substance

Question 10

Heat

Answer 10

the total kinetic energy of a substance

Question 11

Units of heat

Answer 11

Joules (J) or kilojoules (kJ)

Question 12

Specific heat capacity

Answer 12

the joules of heat that are needed to raise the temperature of one gram of a substance by one Kelvin

Question 13

units of specific heat capacity

Answer 13

J/g/K

Question 14

q/delta H/energy change =

Answer 14

mc delta T
M = mass of the substance being heated
C = SHC
Delta T = temperature change
Unit of q is J

Question 15

SHC calculations could be inaccurate due to:

Answer 15

Lack of insulation

Heating the container/vessel

Question 16

Ways to improve accuracy of SHC calculation:

Answer 16

Insulate calorimeter

Use a lid on the calorimeter

Question 17

Which reactions have a negative enthalpy change (negative delta H)?

Answer 17

neutralisation, combustion

Question 18

Standard enthalpy change of formation

Answer 18

energy change when 1 mole of a substance is formed from its elements in their standard state

Question 19

Standard state

Answer 19

pure form of the substance at STP

Question 20

Standard enthalpy change of combustion

Answer 20

energy change when 1 mole of a substance is burnt at STP

Question 21

Enthalpy of formation of oxygen

Answer 21

zero

Question 22

Enthalpy change of a reaction =

Answer 22

enthalpy of formation of the products - enthalpy of formation of the reactants

Question 23

Lower energy means (more/less) stable

Answer 23

more

Question 24

Average bond enthalpy

Answer 24

the energy needed to break one mol of a bond in a gaseous molecule averaged over similar compounds

Question 25

Average bond enthalpy calculations

Answer 25

find the enthalpy for each compound, ones on the left are positive, ones on the right are negative, then sum up

Question 26

Why are ozone bonds easier to break than oxygen bonds?

Answer 26

Ozone has a resonance structure, so the bonds average out to 1.5, which makes it easier to break than O2, which has a double bond