Hess’s Law (CIE A Level Chemistry)

A student calculated the standard enthalpy change of formation of propane, C₃H₈, using a method based on standard enthalpy changes of combustion.

He used correct values for the standard enthalpy change of combustion of propane (–2220 kJ mol^–1) and hydrogen (–286 kJ mol^–1) but he used an incorrect value for the standard enthalpy change of combustion of carbon. He then performed his calculation correctly. His final answer was –158 kJ mol^–1.

What did he use for the standard enthalpy change of combustion of carbon?

Given the following enthalpy changes,

                            I₂ (s) → I₂ (g)                          ∆H^Ɵ = +38 kJ mol^–1

                            I₂ (g) + 3Cl₂ (g) → 2ICl₃ (s)    ∆H^Ɵ = –214 kJ mol^–1

What is the correct value for ∆H_f^θ of iodine trichloride, ICl₃ (s)?

Using the following information:

                       CO (g) +  O₂ (g)   → CO₂ (g)            ∆H^θ  = –283 kJ mol^–1

                       H₂ (g) +  O₂ (g)   → H₂O (I)              ∆H^θ  = –286 kJ mol^–1

                       H₂O (g)   → H₂O (I)                              ∆H^θ = –44 kJ mol^–1

What is the enthalpy change, ∆H^θ, for the following reaction? 

CO₂ (g) + H₂ (g) → CO (g) + H₂O (g)

Iodine trichloride, ICl₃, is made by reacting iodine with chlorine.

I₂ (s) + Cl₂ (g)  2ICl (s) ;    ∆H^o = +14 kJ mol^–1

ICl (s) + Cl₂ (g)  ICl₃ (s) ;   ∆H^o = –88 kJ mol^–1

By using the data above, what is the enthalpy change of the formation for solid iodine trichloride?

The first stage in the industrial production of nitric acid from ammonia can be represented by the following equation.

4NH₃ (g) + 5O₂ (g) ⇌ 4NO (g) + 6H₂O (g)

Using the following standard enthalpy change of formation data, what is the value of the standard enthalpy change ∆H_f^θ for this reaction?

Compound	∆Hfθ /kJ mol–1
NH3 (g)	-51.3
NO (g)	+92.2
H2O(g)	-239.6

Titanium occurs naturally as the mineral rutile, TiO₂. One possible method of extraction of titanium is to reduce the rutile by heating with carbon.

TiO₂ (s) + 2C (s) → Ti (s) + 2CO (g)

The standard enthalpy changes of formation of TiO₂ (s) and CO (g) are –890 kJ mol^-1 and –105 kJ mol^-1 respectively.

What is the standard enthalpy change of the extraction of titanium?

The combustion of ethanol (C₂H₅OH) is increasingly being used to fuel cars. 

The standard enthalpy change of formation of carbon dioxide is –382 kJ mol^–1. 

The standard enthalpy change of formation of water is –275 kJ mol^–1.

The standard enthalpy change of formation of ethanol is −266kJ mol^–1. 

What is the standard enthalpy change of combustion of ethanol?