Chemical Energetics

Question 1

exothermic vs endothermic

Answer 1

1. heat given out vs heat taken in
2. UP temp surroundings vs DOWN
3. e.g. freezing vs evaporation

Question 2

energy unit

Answer 2

energy measured in joules

Question 3

define energy change (q)

Answer 3

energy released/absorbed during rxn when any amnt reactants reacted
J/kJ

Question 4

define enthalpy change (triangle H)

Answer 4

• energy released/absorbed during rxn according to stoichmetric ratio of reactants used & products formed in a balanced eqn (per mole eqn)
• • sign = released & + sign = absorbed
• calculation: energy change (q)/no. moles limiting reagent * stoichmetric coeff of limiting reagent
• energy absorbed + energy released
  J mol^-1 / kJ mol^-1

Question 5

explanation 4 energy changes

Answer 5

chemical rxn involves breaking of chemical bonds in reactant particles & formation of new bonds in product particles; involves energy changes

Question 6

define bond energy

Answer 6

avg energy absorbed to break 1 mole of colvalent bond in gaseous state