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What does system mean in a chemical reaction?
the atoms and bonds involved in the reaction
Explain the law of conservation.
the amount of energy in an isolated system stays the same / energy cannot be created or destroyed, only transferred from one system to another
Breaking bonds is...?
endothermic
Making bonds is…?
exothermic
What is an endothermic reaction?
reaction with an overall positive enthalpy change
products > reactants
What is an exothermic reaction?
reaction with an overall negative enthalpy change
reactants > products
What type of reaction is shown in this enthalpy profile?
exothermic
What type of reaction is shown in this enthalpy profile?
endothermic
What is activation energy (Ea)?
the minimum energy required for a reaction to take place
Which way does the arrow for Ea point in an enthalpy profile diagram?
always points upwards
What are the standard conditions?
101 kPa / 1atm
298K / 25°C
1 moldm⁻³
What does ‘standard state’ mean?
the state an element or compound exists at under standard conditions
What is standard enthalpy change of formation?
enthalpy change when 1 mol of a compound is formed from its constituent elements in their standard stated under standard conditions
What is standard enthalpy change of combustion?
enthalpy change when 1 mol of a substance reacts completely with oxygen with all reactants and products in their standard states
What is standard enthalpy change of neutralisation?
enthalpy change when 1 mol of water is formed in the reaction between an acid and a base, under standard conditions with all reactants and products in their standard states
What is standard enthalpy change of reaction?
enthalpy change accompanying a reacion in the molar quantities shown in the chemical equation in standard conditions with all reactants and products in their standard states
How can you calculate enthalpy change from experimental data?
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 be inaccurate?
heat lost to surroundings
not under standard conditions
reaction may not go to completion
What is average bond enthalpy?
the mean energy required to break 1 mol of bonds in gaseous molecules
How do you calculate enthalpy change of reaction using average bond enthalpies?
reactants - products (B.E. R-P)
Why are bond enthalpies less accurate than standard energy of combustion/formation?
enthalpies are a mean for the same bond in a different molecule whereas standard enthalpies are specific to the molecule
Note 
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