Hess's Law

Which of the following reactions enthalpy change cannot be directly measured

• Formation of methane

• Formation of carbon monoxide

• Complete combustion of carbon

• Combustion of methane

How would you determine the enthalpy change in a reaction?

• Eh = cmΔT and ΔH = Ehn

• Eh = cmΔ/T and ΔH = Ehn

• Eh = cmΔT and ΔH = Eh/n

• Eh = cmΔT and ΔH = Eh/T

If the formation of methane is 1500 and the combustion of methane is 1300 and the enthalpy of combustion of carbon is 40, what is the enthalpy of the combustion of hydrogen?

• 2840

• 160

• 140

• 40

Hess's Law states that...

• all reactions are reversible

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

• the direct route results in a greater enthalpy change

• the indirect route results in a lower enthalpy change as energy is lost in the second step

ΔH value in an endothermic reaction is a positive number.

• True
• False

The diagram represents which type of reaction

• endothermic
• exothermic

ΔH value in an exothermic reaction is a negative number.

• True

• False

What symbol represents Enthalpy change?

• ΔH

• ΔT

• ΔG

• ΔS

(Hess's Law)Calculate the ∆H for the following reaction: 2H₂O₂ →  2H₂O  + 1 O₂ 
You are given these two equations:
2H₂  +  O₂ → 2H₂O            ∆H  =  -572 kJ
H₂  +  O₂  →  H₂O₂            ∆H  =  -188 kJ 

• ∆H  =  -948 kJ 
• ∆H  =  -196 kJ 
• ∆H  =  -384 kJ 
• ∆H  =  -188 kJ