Core Practical 8

Question 1

Why can the enthalpy change of a thermal decomposition reaction not be measured directly?

Answer 1

As thermal energy must be supplied for the reaction to occur the temperature change measured is not only due to decomposition.

Question 2

Why may an experimental value for an enthalpy change be different to the theoretical value?

Answer 2

Heat loss to apparatus/ surroundings
Incomplete combustion
Evaporation of water/alcohol
Non-standard conditions

Question 3

How can you prevent heat loss to surroundings/apparatus?

Answer 3

Use polystyrene cup with lid inside glass beaker to insulate

Avoid large temperature differences between surroundings and calorimeter

Question 4

Other than preventing heat loss how else can the accuracy of the experiment be improved?

Answer 4

Stir solution so temp is evenly distributed
use greater concentrations and masses so greater temperature change thus less uncertainty
red thermometer at eye level