Enthalpy changes
The symbol for an endothermic reaction is
+∆H
The symbol for an exothermic reaction is
-∆H
The standard conditions are
100kPa, 298K and the standard state of the substance (e.g. oxygen as gas)
The ionic equation for all strong base and strong acid reactions is
H⁺ + OH⁻ = H₂O
Enthalpy change is defined as the
amount of energy released/taken in during a chemical reaction (cannot be measured)
In enthalpy change reactions the calculation rule you use is
bond breaking - bond making (always remember sign)
Bond breaking is
endothermic
Enthalpy change of combustion is defined as the
enthalpy change associated with the complete combustion of 1 mole of substance
Enthalpy change of formation is defined as the
enthalpy change associated with the formation of 1 mole of a compound from its elements
The enthalpy change of neutralisation is defined as the
enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between acid and base
Enthalpy change of reaction is defined as the
enthalpy change for a reaction when molar quantities of reactants react together
Bond making is
exothermic
Enthalpy is defined as the
measure of heat energy present in a chemical reaction
Activation energy is defined as the
minimum energy required for a reaction to take place also meaning the energy required to break bonds
Delta H is calculated by doing
products - reactants (can be + or -)
To calculate ∆neutH you do
q / moles of water (unit of q will give same unit of ∆neutH)
An exothermic reaction is one that
releases energy into its surroundings
An endothermic reaction is one that
taken in energy from its surroundings
The formula to calculate enthalpy change of combustion is
∆H1 - ∆H2
To formula to calculate enthalpy change of formation is
∆H2 - ∆H1
The symbol for enthalpy change under standard conditions is
∆H^θ
Because all strong base and strong acid reactions have the same ionic equation the enthalpy change of neutralisation will always be
∆neutH = -57
