Topic 8 Flashcards
Enthalpy change of reaction
The enthalpy change of a reaction according to the molar quantities in the equation under standard conditions
Example of endothermic reaction
Thermal decomposition of calcium carbonate
CaCO3(s) –> CaO(s) +CO2(g)
Example of exothermic reaction
Combustion of ethane
C2H4(g) + 3.5O(g) –> 3H20(l) + 2CO2(g)
Enthalpy change of neutralisation
The enthalpy change when an acid and alkali react to form 1 mole of water under standard conditions
Enthalpy change of combustion
The enthalpy change when 1 mole of substance is completely burned in oxygen to make CO2 and H20, under standard conditions
Enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions.
Bonds broken
endothermic
Bonds made
exothermic
Bond enthalpy
Amount of energy needed to break 1 mole of a bond type in a molecule in the gaseous state
Enthalpy change =
Total energy to break bonds - Total energy released forming bonds
Calorimetry
1) Fuel burned to raise temp of water by specific amount.
2) Weigh fuel before and after burning.
3) Energy of fuel is transferred into water.
How to prevent heat loss in calorimetry
Lid placed on top of beaker with water.
Wind shields placed by the flame to prevent a draught moving the flame.
Energy transferred can be calculated using:
q=mcdeltaT
Enthalpy=
q/moles
Hess’s Law
The total enthalpy change of a reaction is independent of the route taken
Hess’s Cycle: Formation
Reactants –> Products
(Arrows facing upwards)
Elements in
their standard states
Hess’s Cycle: combustion
Reactants/elements –> products
(Arrows facing downwards)
CO2+H20
