Unit 3: Chemical Energy

Question 1

Enthalpy

Answer 1

Eh= energy (enthalpy)
C= specific heat capacity (water 4.18)
M= mass of water in kg (take 1ml as 1g)
^T= change in temperature

Eh=cm^T

Complete combustion CO² + H²O

Question 2

Formulas for enthalpy of combustion

Answer 2

1. Calculate Eh=cm^T
2. Calculate n m=nxfm
3. Use n and Eh to calculate combustion
   (1xEh)/n
   Almost always minus!

Question 3

Hess’s law

Answer 3

The enthalpy change for a reaction depends only on the initial and final states of the reaction and is independent of the route by which the reaction may occur

Question 4

Bond enthalpies

Answer 4

Energy required to break one mole of bonds in a diatomic molecule.

Question 5

Mean bond enthalpies

Answer 5

Average energy required to break one mole of bonds, for a bond that occurs in a number of compounds