energetics (paper 1) 55-57

Question 1

what is meant by the term exothermic reaction

Answer 1

a reaction that gives out energy to surroundings, usually in the form of heat and shown by a rise in temperature

Question 2

is bond breaking an exothermic or endothermic reaction

Answer 2

endothermic

Question 3

if a reaction is exothermic does the temperature rise or fall

Answer 3

rise

Question 4

give 2 examples of exothermic reactions

Answer 4

• condensing steam to water
• adding potassium to water

Question 5

what is meant by the term endothermic reaction

Answer 5

a reaction that takes energy in from the surroundings, shwon by a fall in temperature

Question 6

what is the change in energy called

Answer 6

the enthalpy change

Question 7

what is meant by the term enthalpy change

Answer 7

the overall change in energy in a reaction is called the enthaply change

Question 8

what is the symbol for enthalpy change

Answer 8

ΔH

Question 9

what are the units for enthalpy change (ΔH)

Answer 9

kJ/mol

Question 10

what is the value of an enthalpy change like if the reaction is EXOthermic

Answer 10

the value will be negative because the reaction gives OUT energy

Question 11

what is the value of an enthalpy change like is the reaction is ENDOthermic

Answer 11

the value will be positive beacuse the reaction takes IN energy

Question 12

what is the equtation for enthalpy change (just energy release overall = Q)

Answer 12

Q = mass of liquid heated x specific heat capacity x change in temperature

Question 13

what is the equation for energy release per mole (enthalpy change per mole)

Answer 13

Q/mol

Question 14

what are the different types of enthalpy change

Answer 14

• enthalpy of combustion
• enthalpy of displacement
• enthalpy of neutralisation
• enthalpy of dissolving

Question 15

what is the term for the process used to measure enthalpy change

Answer 15

calorimetry

Question 16

which three types of calorimetry are have the same method

Answer 16

• enthalpy of displacement
• enthalpy of neutralisation
• enthalpy of dissolving

Question 17

which type of calorimetry has a different method

Answer 17

enthalpy of combustion

Question 18

what are the problems with normal calorimetry

Answer 18

• heat loss to the surroundings, from the can = insulated the can, using a lid
• incomplete combustion resulting in a build up of soot (insulator)
• alcohols are volatile so mass can be lost as soon as lid is removed
• activation energy can be too high or too slow so bond energy calculations must be used instead

Question 19

desribe the calorimetry method for dissolving, displacement and neutralisation

Answer 19

• put 25cm^3 of acid and base into seperate beakers
• place the beakers in a waterbath to 25°C until they are the same temperature
• add acid and base into insulated, polystyrene cup with a lid with a thermometer
• take the temperature of the mixture every 30sec and record the highest temperature
• repeat 3 more times

Question 20

describe the calorimetry method for combustion

Answer 20

• weight the spirit burner, with its lid on, on the balance and record the mass
• measure out 100cm^3 water and pour into the calorimeter (copper can)
• set up the equipment as shown in the diagram by clamping the calorimeter a good hieght above the spirit burner
• record the starting temperature of the water
• light the burner and stir the water, monitoring the temperature until 100°C
• estinguish the flame and re-weigh the spirit burning
• calculated the energy change and the enthalpy change