TOPIC 8: Energetics 1

Question 1

Enthalpy🔺H

Answer 1

Heat change at constant pressure kJmol^-1
Standard conditions 298K, 25C

Question 2

Endothermic vs exothermic

Answer 2

Endo
Reactions absorb energy from surroundings so +H (Eproducts>)
Bonds broken: more E needed to break

Exo
Reactions release energy to surroundings so -H (Ereactants>)
Bonds formed: more E released when forming

Question 3

Standard enthalpy change of …
(Under standard conditions)

Answer 3

Reaction
according to molar quantities in equation

Neutralisation
acid and alkali react to form 1 mole of water

Combustion
1 mole of a substance is completely burned in oxygen to make CO2 and H2O

Formation
1 mole of a compound is formed from its elements in their standard conditions

Question 4

Bond enthalpy

Answer 4

Amount of energy needed to break 1 mole of a bond type in a molecule in the gaseous state

Normally a mean as are all different

Question 5

Enthalpy change

Answer 5

Energy to break bonds - energy released forming bonds

Question 6

Q = mcT

Answer 6

Q heat energy lost/gained (J)
m mass of solution/water (g) if solution assume 1 cm^3 is 1g
c specific heat capacity (water 4.18Jg-1K-1)
T temperature change (K/C)

Question 7

HESS’S LAW

Answer 7

Total enthalpy change of a reaction is independent of the route taken