Enthalpy Changes Flashcards
Define enthalpy
the heat content stored in a chemical system
How is energy given out in a chemical system after bonds in reactants break?
Energy is given out when new bonds form in the product.
What is the reaction called when energy is needed to break bonds, which is then released when these bonds are made?
endothermic reaction
In a reaction, if more energy is used when bonds are made then taken in when bonds are broken. What type of reaction is it?
endothermic reaction
What can help illustrate enthalpy changes in reaction?
Enthalpy profiles
What does an exothermic reaction enthalpy profile show?
it shows that the enthalpy of the products is lower than the enthalpy of the reactants.
It also shows that heat is given out to the surroundings.
What does an endothermic reaction enthalpy profile show?
In endothermic reactions, the enthalpy of the products is greater than that of the reactants.
This also shows that heat is absorbed from the surroundings.
What does enthalpy refer to?
heat energy
Do reactions happen spontaneously?
They don’t tend to
What is needed to start a reaction?
An input of energy.
What is that input energy called to start a reaction?
Activation Energy
What can enthalpy profiles show with the activation energy in both endothermic and exothermic reactions?
The amount of activation energy needed for both reactions to occur and the difference in the energy for both reactions
Define standard enthalpy change of formation
the enthalpy change that occurs when one mole of a compound forms from its elements under standard conditions.
Define standard enthalpy change of combustion
the enthalpy change that occurs when one mole of a compound completely combusts in oxygen under standard conditions
Define standard enthalpy change of neutralisation
the enthalpy change that occurs when an acid is neutralised by a base forming one mole of water under standard conditions.
