Hess Law, Find enthalpy change of combustion reaction through enthalpy change of 2 other reactions

Question

Chemistry: Find the enthalpy change of the reaction: 2KHCO3 --> CO2 + H2O + K2CO3 ΔH1 Through using these equations and constructing a Hess's diagram: K2CO2 + 2HCl --> 2KCl + H2O + CO2 ΔH2 KHCO3 + HCl --> KCl + H2O + CO2 ΔH3

Answer 1

2KHCO3 --> CO2 + H2O + K2CO3  Target equation

 

Reverse equation for ∆H2 to get 2KCl + H2O + CO2 ==> K2CO2 + 2HCl and reverse the sign for ∆H2

Multiply equation for ∆H3 by 2 to get 2KHCO3 + 2HCl ==> 2KCl + 2H2O + 2CO2 and multiply ∆H3 by 2

Add equations to get 2KHCO3 + 2HCl + 2KCl + H2O + CO2 ==> 2KCl + 2H2O + 2CO2 + K2CO2 + 2HCl

Cancel like terms on each side to get 2KHCO3 ==> H2O + CO2 + K2CO2  which is the target equation.

You then add the ∆H values to get the ∆H for the target equation.  Remember to reverse the sign for ∆H2 and double the value for ∆H3.

 

Can't actually construct the Hess diagram here because of web site limitations, but you should be able to do so by following the above description.