2.1 Developing Fuels

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Developing Fuels
1.1 Getting energy from fuels
Exothermic Endothermic
Gives out heat energy Requires heat energy
Negative ^H Positive ^H
Energy given out during bond breaking Energy given out during bond breaking
> Energy required for bond formation < Energy required for bond formation
Enthalpy level diagram: Enthalpy level diagram:
Enthalpy change ­ the enthalpy change in a chemical reaction gives the quantity of energy
transferred to or from the surroundings when the reaction is carried out in an open container
System ­ the reactants and products
Surroundings ­ where the reaction happens e.g. test tube/environment
Standard Conditions
­ 298K or 25o
C and 101kPa or 1atm and a conc of 1 mol dm1
Standard States the physical state of a substance under standard conditions this may be a pure
solid, liquid or gas
o
Standard Enthalpy Change for a reaction ­ (^H r ) the enthalpy change when molar quantities or
reactions as stated in the equations react together under standard conditions. Units: kJ mol1
1
Energy Transfer Equation
: Q (kJ) = m(g) x c (J g1 K) x ^t (K)
o
Standard Enthalpy Change of combustion ­ (^H c ) the enthalpy change when 1 mole of substance
is burnt completely in oxygen under standard conditions and in standard states. It is always
negative as combustion is an exothermic reaction. Units: kJ mol1
Complete Combustion CH4 + 2O
2
CO 2 + 2H
2O
Incomplete Combustion CH4 + 1½O 2 CO + 2H 2O Emits soot (C), Carbon monoxide
CH4 + O2 C + 2H 2O (CO) and unburnt hydrocarbons
o
Standard Enthalpy Change of Formation ­ (^Hf ) the enthalpy change when 1 mole of substance is
formed from its elements under standard conditions and in standard states. It can be positive or
negative. Units: kJ mol1

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H2(g) + ½
O
2(g) 1H2O(l)
o
Standard Enthalpy Change of Neutralisation ­ (^H neut ) the enthalpy change when one mole of
hydrogen ions react with one more of hydroxide ions to form one mole of water under standard
conditions and in solutions containing 1 mol dm3
1
Na+OH(aq) +
1H+Cl(aq) NaCl(aq) + 1H
2O (l)…read more

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