5.2 Energetics
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What is meant by the term enthalpy change?
heat energy released or absorbed per mole
What does endothermic mean?
heat energy absorbed
What does exothermic mean?
heat energy released
What does breaking bonds do?
absorbs energy
What type of reaction is bond breaking?
endothermic
What does making bonds do?
releases energy
What type of reaction is bond making?
exothermic
When is enthalpy change positive?
endothermic reactions
When is enthalpy change negative?
exothermic reactions
What requires more energy to break?
stronger bonds
What releases more energy when made?
stronger bonds
How can enthalpy change be calculated?
bonds broken - bonds made
How is a reaction profile diagram different to an energy level diagram?
shows path of reaction from reactants to products
When is more energy released?
exothermic reaction
When is less energy released?
endothermic reaction
When is more energy absorbed?
endothermic reaction
When is less energy released?
exothermic reaction
What is calorimetry?
experimental method used to measure enthalpy change`
What happens in an exothermic calorimetry reaction?
reaction releases heat energy absorbed by water temperature of water increases
What is the equation for heat energy Q (J)?
Q = mcΔT
What is the equation for enthalpy change ΔH (kj/mol) ?
ΔH = - Q / moles
What is heat energy measured in?
Joules
What is enthalpy change measured in?
kilojoules / mole
What is the simplest type of calorimetry?
combusting a fuel to heat up water