5.3 Exothermic, Endothermic, Delta H Energy Profiles [SL IB Chemistry]
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Define the terms exothermic reaction,
Define the terms exothermic reaction, endothermic reaction and standard enthalpy change of reaction. An exothermic reaction releases energy (heat) to the surroundings and therefore feels warm. There are 2 possible definitions:
a) The energy of the products is less than the energy of the reactants -- so this difference in energy is released.
b) The bonds in the product are stronger/more numerous than the bonds in the reactants. Making these extra bonds releases the energy to the surroundings
.
An endothermic reaction is one where the products have a higher energy than the reactants and therefore energy (heat) must have been absorbed from the surroundings-- the reaction feels cold -- bonds in the product are weaker/less numerous than in the reactants. The energy taken in from the surroundings went to break these extra bonds. Removing energy from the surroundings leaves it feeling colder.
Standard enthalpy change is the heat energy transferred under standard conditions—pressure 101.3 kPa, temperature 298 K. Only delta H can be measured, not H for the initial or final state of a system.
14 سال پیش
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