Thermochemistry Flashcards
What is kilogram calorific value
Kilogram calorific value is the heat energy produced when 1 kg of a fuel is burned completely in oxygen.
Define bond energy
Bond energy is the average energy required to break one mole of covalent bonds and completely free or separate the neutral atoms from each other.
What is involved in a bomb calorimeter
- A KNOWN MASS of the substance is placed in the crucible inside the bomb calorimeter.
- the bomb /steal container containing the Crucible is filled with OXYGEN.
- the bomb is placed in a KNOWN QUANTITY of water inside the calorimeter.
- substance is ignited electrically and the rise in temperature of the water is measured.
Define heat of combustion
Heat of combustion is the heat change which occurs when one mole of a compound is burned in excess oxygen.
AH = - (exothermic )
Define heat of formation
Heat of formation is the heat change which occurs when one mole of a compound is formed from its elements in their standard states.
What is a neutralisation reaction?
A neutralisation reaction is a reaction between an acid and a base.
Essential reaction is : H+. + OH- _> H2O
AH= - i.e. Neutralisation reaction is exothermic
Define heat of neutralisation.
Heat of neutralisation is the heat change which occurs when 1 mole of H+ ions from an acid react with 1 mole of OH- ions from a base.
AM= -
Does the AH value obtained vary with the type of acid used.
(A) Strong acids e.g. HCI, H2SO4, HNO3.
The AH value is the same for each of the above strong acids.
Reason: Strong acids dissociate fully in an aqueous solution and from H+ ions.
Essential reaction which occurs: H+ +OH- -> H2O
(B) Weak acids e.g. CH3COOH
The AH value will be lower.
Reason: Weak acids do not dissociate fully in water.
Some of the heat produced during the neutralisation reaction is required to dissociate the acid molecules and form 1 mole of H+ ions.
Less heat released to the surroundings.
