Chemical Energetics

Question 1

Define the enthalpy of a substance.

Answer 1

The energy content of a substance.

Question 2

State the symbol and unit for enthalpy charge.

Answer 2

Symbol: ΔH
Unit: kJ mol ^-1

Question 3

State the differences between endothermic and exothermic reactions, in terms of:
1. energy absorption or release
2. temperature of surroundings
3. enthalpy of the system
4. enthalpy content of products VS reactants
5. energetic stability of products VS reactants
6. sign of ΔH

Answer 3

1. Endothermic reaction: The reacting system absorbs heat from the surroundings.
   Exothermic reaction: The reacting system releases heat to the surroundings.
   2.
   Endothermic reaction: The temperature of the surrounding decreases.
   Exothermic reaction: The temperature of the surrounding increases.
   3.
   Endothermic reaction:
   The enthalpy of the system increases.
   Exothermic reaction:
   The enthalpy of the system decreases.
   4.
   Endothermic reaction:
   The enthalpy content of products is higher than that of reactants.
   Exothermic reaction:
   The enthalpy content of products is lower than that of reactants.
   5.
   Endothermic reaction: The products are less stable than the reactants.
   Exothermic reaction: The products are more stable than the reactants.
   6.
   Endothermic reaction: positive
   Exothermic reaction: negative