Tutorial 5 Answer Presentation

Hu Peiyu12S7F

Question 2

• a) Hess’s law states that the enthalpy change (ΔH) of a particular reaction is determined only by the initial and final state of the system regardless of the pathway taken.

Question 2

• b) i) K2CO3+2HCl→2KCl+H2O+CO2

• ii) Heat evoved: q=m c∙ ∙ΔH=V/ρ c∙ ∙ΔT =30.0/1.0*4.2*5.2 =655J ΔHr=-q/n=625J/0.020mol=-32.8KJ/mol

Question 2

• iii) because HCl is in excess in this reaction, the concentration of it need not to be exact.

Question 2

• c) i) KHCO3+HCl→KCl+H2O+CO2

• ii) Heat absorbed: q=m c∙ ∙ΔH=m c∙ ∙ΔT =30.0*4.2*3.7 =466.2 ΔH=466.2/0.020=23.3KJ/mol

Question 2

• d) Energy/ kJmol-1

ΔH=-32.8kJ

KCl+H2O+CO2

K2CO3+2HCl

KHCO3+HCl

ΔH=23.3kJ

Hd=?

Question 2

• By Hess’s law• Hd(KHCO3)=23.3kJ-(-32.8kJ)=56.1kJ