Physical Chemistry - Energetics

Question 1

what is an exothermic reaction?

Answer 1

a chemical reaction in which heat energy is given out

Question 2

what is an endothermic reaction?

Answer 2

a chemical reaction in which heat energy is taken in

Question 3

what does calorimetry allow?

Answer 3

for the measurement of the amount of energy transferred in a chemical reaction to be calculated

Question 4

how would you do a calorimetry experiment for a displacement/dissolving/neutralisation reaction?

Answer 4

magnesium displacing copper from copper(II) sulfate:
- 50 cm³ of copper(II) sulfate is measured and transferred into a polystyrene cup
- the initial temperature of the copper sulfate solution is measured
- magnesium is added and the maximum temperature is measured
- temperature rise is then calculated

Question 5

why is the cup polystyrene in a calorimetry experiment?

Answer 5

polystyrene is an insulator which reduces heat loss

Question 6

how would you do a calorimetry experiment for a combustion reaction?

Answer 6

ethanol being burnt in a small spirit burner:
- initial mass of the ethanol and spirit burner is measured
- 100cm³ of water is transferred into a copper container and the initial temperature is measured
- the burner is placed under the copper container and lit
- the water is stirred constantly with the thermometer until the temperature rises by a set amount
- the flame is extinguished and the maximum temperature of the water is measured
- the burner and the remaining ethanol is reweighed

Question 7

how would you calculate heat energy change?

Answer 7

amount of energy transferred = mass x specific heat capacity x temperature rise
Q = mcΔT

Question 8

how do you calculate the molar enthalpy change?

Answer 8

molar enthalpy change = amount of energy transferred (Q)/number of moles