Enthalpy Changes - 3
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Explain the law of conservation
The amount of energy in an isolated system remains the same. Energy cannot be destroyed or created =, it can only be transferred from one to another
What energy change is breaking bonds associated with
Energy is taken in to break bonds Endothermic reaction
What energy change is associated with making bonds
What energy is released to make bonds exothermic reaction
What is an endothermic reaction
A reaction with an overall positive enthalpy change Enthalpy products > enthalpy of reactants
What is an exothermic reaction
A reaction with an overall negative enthalpy change enthalpy of products < enthalpy of reactants
Define activation energy
The minimum energy required for a reaction to take place
What are standard conditions
100KPa 298K
Define enthalpy change of formation
The energy change that takes place when 1 mole of a compound is formed from its elements in their standard state under standard conditions
Define enthalpy change of combustion
The energy change that takes place when 1 mole of a substance is completely combusted with oxygen
Define enthalpy change of neutralisation
the energy change that takes place when 1 mole of water is formed from a neutralisation reaction
What does enthalpy change of reaction mean
The energy change associated with a given reaction
What is the equation for calculating enthalpy change
q = mc∆T
What are the advantages of using a bomb calorimeter
Minimises heat loss Pure oxygen used, ensures complete combustion
Why might experimental methods for enthalpy determination not be accurate
Heat is lost to the surroundings Not in standard conditions reaction may not go to completion
What does average bond enthalpy mean
the mean energy required to break 1 mole of bonds in gaseous molecules
Why will using bond enthalpies not be as accurate as using standard enthalpy of combustion
Bond enthalpies are a mean for the same bond across different molecules Standard enthalpy of combustion apply just to that molecules
How to calculate enthalpy change of reaction using average bond enthalpies
Sum of bond enthalpies of reaction - Sum of bond enthalpies products