Developing Fuels

Developing Fuels Revision questions and suggested answers

1. Define ΔHfθ and ΔHcθ
ΔHfθ the enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states measured under standard conditions
ΔHcθ the enthalpy change when 1 mole of a compound undergoes complete combustion measured under standard conditions

2. Write an equation for the enthalpy of formation of butane C4H10

4C(s) + 5H2(g)  C4H10(g)
3. Write an equation for the enthalpy of combustion of butane C4H10
C4H10(g) + 6 ½ O2(g)  4CO2(g) + 5 H2O (l)

4. Which has the most exothermic enthalpy of combustion methane or octane and why?
Octane as more energy released than when bonds are made than broken than with methane
5. Calculate the enthalpy change from an experiment in kJmol-1.
a. e.g. the temp of 100g of water rose by 12 degrees C when 1g of methanol was completely combusted. The specific heat capacity of water is 4.2 Jg-1K-1
∆H = - 100 X 4.2 X 12 / 1/32 (/ moles methanol) then / 1000 = - 161 kJ mol-1

6. State Hess’s law and use a Hess’s law cycle to find ΔHθf of CH4 if given the ΔHθc of C , ΔHθcH2.and ΔHθc CH4
a. Hint : first write an equation for the enthalpy of formation of methane.
Enthalpy change is independent of the route taken ΔHθf of CH4 C(s) + 2H2(g)  CH4(g) ΔHθc of C ΔHθc CH4 + 2ΔHθcH2 CO2 (g) + 2H2O(l)
7. Which is exothermic bond making or bond breaking?
Bond making exo

8. Give an example of an
i. Alkane Butane C4H10 ii. Alkene Ethene C2H4 iii. Cycloalkane Cyclohexane C6H12 iv. Alcohol Ethanol C2H5OH
v. Ether Methoxy methane CH3OCH3

9. What does an aromatic compound contain? Note all other compounds are aliphatic
A benzene ring

10. Give examples of all 3 types of structural isomerism
i. Chain