Enthalpy

Question 1

Endothermic reactions

Answer 1

Enthalpy of products> enthalpy of reactants

System absorbs heat from surroundings: More energy taken in making bonds, than released breaking bonds.

Give +/ve values

Question 2

what are standard conditions

Answer 2

100kpa
298K (25C)
1moldm-3

Question 3

standard enthalpy of reaction

Answer 3

enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions

Question 4

enthalpy change of formation

Answer 4

enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions with standard states

Question 5

enthalpy change of combustion

Answer 5

enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions

Question 6

enthalpy change of neutralisation

Answer 6

energy change that accompanies the reaction of an acid to a base to form one mole of H2O under standard conditions and states

Question 7

Reasons for combustion experiment value being less exothermic than data book

Answer 7

- heat lost to surroundings 
  other than water 
- incomplete combustion 
- evaporation of methanol 
  from the wick 
- non standard conditions

draught screens and oxygen could minimise errors from heat loss and incomplete combustion

Question 8

calculating energy change

Answer 8

Q= Mc🔺T in Joules

Mass of surroundings x specific heat capacity x difference in temperature

Question 9

Activation energy

Answer 9

Minimum energy required to start a reaction by breaking of bonds

Question 10

Average Bond enthalpy

Answer 10

energy required to break one mole of a specified bond in a gaseous molecule

Question 11

how to calculate enthalpy change from average bond enthalpies

Answer 11

Delta change of reaction = sum of bond enthalpy in reactants - bond enthalpy in products

Question 12

Formula for enthalpy change

Answer 12

🔺H = Q/n