Enthalpy

Question 1

State the conditions of temperature and pressure used for standard enthalpy
measurements.

Answer 1

25°C
AND
100 kPa

Question 2

Why do Br2 and I2 not exist in the gaseous state under standard conditions?

Answer 2

(because energy is needed to break) induced dipole
dipole interactions / London forces between molecules

Question 3

Explain, in terms of bond breaking and bond forming, why a reaction can be exothermic.

Answer 3

More energy is released by forming bonds
than energy required when breaking bonds

Question 4

Explain, in terms of bond breaking and bond forming, why a reaction can be endothermic.

Answer 4

More energy is required when breaking bonds than energy released by forming bonds

Question 5

Define standard enthalpy change of combustion.

Answer 5

(enthalpy change that occurs) when one mole of a substance completely combusts OR reacts fully with oxygen

Question 6

What is meant by the term average bond enthalpy?

Answer 6

(Average enthalpy change) when one mole of bonds of (gaseous covalent) bonds is broken

Question 7

What is meant by the term standard enthalpy change of formation?

Answer 7

(Enthalpy change) when one mole of a compound is formed from its elements

Question 8

Explain, why the answer to (ii) is the enthalpy change of neutralisation.

Answer 8

1mole of water has been formed