Ch10 Enthalpy changes Flashcards
Enthalpy change
the difference between the enthalpy of reactants and the enthalpy of products
ΔH = enthalpy products - enthalpy reactants
Exothermic reaction
ΔH is negative
- reactants have lost energy and it has been transferred from mixture to surroundings
Endothermic reaction
ΔH is positive
- products have higher energy than reactants and heat is taken from surroundings
activation energy
minimum energy needed for a reaction to take place
bond breaking
endothermic(requires energy)
bond formation
exothermic (returns energy)
Bond enthalpy
enthalpy change required to break and separate 1 mol of bonds in the molecules of a gas so that the resulting gaseous(neutral) particles exert no forces upon each other
energy equation
q = mcΔt
specific heat capacity
heat required to increase temperature of 1g of substance by 1°C
shc of water
4.18
reliability of thermochemical experiments
- lack of precision of measuring equipment e.g. thermometer
- heat loss to surroundings
- slowness of reaction
Standard conditions
temp 298K (25°C)
pressure 100KPa
Standard enthalpy change of formation
enthalpy change when 1 mol of a substance is formed from its elements, in their natural state under standard conditions
standard enthalpy change of combustion
enthalpy change when 1 mol of substance is burned completely, in an excess of oxygen, under standard conditions
Standard enthalpy change of neutralisation
enthalpy change when 1 mol of water is formed in a reaction between an acid or a base
