Chemical energetics

Question 1

Standard conditions

Answer 1

Pressure- 1atm or 10^5 Pa (100kPa)

Temperature- 298K or 25C

Question 2

Enthalpy change of formation

Answer 2

The enthalpy change which occurs when one mole of a compound is formed from its elements under standard conditions

Question 3

Enthalpy change of combustion

Answer 3

The enthalpy change which occurs when one mole of a substance undergoes complete combustion under standard conditions

Question 4

Bond energy

Answer 4

Energy required to break 1 mole of similar bonds in a mole of gaseous atoms

Question 5

Calculating enthalpy changes
E=mc🔺T
🔺H= E/n

Answer 5

E= heat energy (J)
m= mass of water (g)
c= specific heat capacity (4.18)(J)
🔺T= Change in temperature (C)

For 🔺H=E/n, E is in kJ not J so remember to convert (divide by 1000)

Question 6

Hess’s law

Answer 6

The total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same