A reaction where heat is given out, as the reactants change to products. As a result temperature rises
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What is an endothermic reaction?
A reaction where heat has been taken in from the surroundings, as the reactants change to products. As a result, there is a drop in temperature
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What is enthalpy change?
When we measure heat energy taken in or given out when there is a chemical or physical change at constant pressure
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Define standard enthalpy of formation
The enthalpy change under standard conditions, when one mole of a compound is formed from its reactants, with a reactants and products in their standard states
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Define standard enthalpy of combustion
The enthalpy change under standard conditions, when one mole of a substance is completely burned in excess oxygen, with all reactants and products in their standard states
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How is enthalpy change measured in a reaction?
Enthalpy change=mass of a substance x specific heat capacity x temperature change
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What does Hess's law state?
The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products
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Define enthalpy of elements
The enthalpies of all elements in their standard states are taken as zero
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What is a bond enthalpy?
The enthalpy change required to break a covalent bond with all species in the gaseous states
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Define mean bond enthalpy
The average value of the bond enthalpy for a given type of bond given from a range of different compounds
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Why is using mean bond enthalpies for calculations not very accurate?
Because mean bond enthalpies are averages. Calculations for specific compounds using them will only give you approximate answers
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Other cards in this set
Card 2
Front
What is an endothermic reaction?
Back
A reaction where heat has been taken in from the surroundings, as the reactants change to products. As a result, there is a drop in temperature
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