3.2.1 enthalpy changes

enthalpy change

the exchange of energy between reactants and surrounding during a reaction

enthalpy change formula

enthalpy of reactants-enthalpy of products

exothermic reaction

negative enthlapy change

endothermic reaction

positive enthlapy change

activation energy

the minimum energy required for a reaction to take place

standard conditions ___pressure, ____temperature, _____concentration

100kPa, 298K, 1.0dm-3

enthalpy change of combustion

the enthalpy change when 1 mole of a substance is burned completed in an excess of oxygen

the enthalpy change when 1 mole of water is formed in a reaction between and acid and a base

enthalpy change of neutralisation

energy released

mass x specific heat x temperature change

exothermic

bonds form

endothermic

bonds break

average bond enthalpy

the enthalpy change required to break 1 mole of bonds in gaseous molecules

-precision of equipment
-heat loss to surroundings
-incomplete reaction
-speed of reaction

problems with measuring enthalpy

-weak acids on partially dissociate so as it is neutralised energy is need to dissociate more H+, so enthalpy change value is lowered
-weak bases need more energy to ionises than weak acids, so enthalpy change is lowered further
-weak acid and weak base reaction have an even lower enthalpy change value

exceptions to enthlapy change of neutralisation