Enthalpy Definitions

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Endothermic
A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings. ΔH is positive.
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Standard enthalpy change of reaction
The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard state. ΔrH⊖.
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Exothermic
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. ΔH is negative.
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Enthalpy
The heat content that is stored in a chemical system.
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Standard enthalpy of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard state. ΔcHΘ
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Activation energy
The minimum energy required to start a reaction by the breaking of bonds.
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Standard enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard state. ΔfHΘ.
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Standard state
The physical state of a substance under standard conditions of 100kPa and a stated temperature (usually 298K).
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Standard conditions
A specified temperature, 1atm of pressure and a 1mol/dm3.
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Conservation of energy
Energy cannot be created or destroyed, only transferred from one form to another or from one object to another.
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Enthalpy profile diagram
A diagram for a reaction that compares the enthalpy of the reactants with the enthalpy of the products.
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Standard enthalpy change of neutralisation
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O, under standard conditions with all reactants and products in their standard states.ΔneutHΘ.
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Card 2

Front

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard state. ΔrH⊖.

Back

Standard enthalpy change of reaction

Card 3

Front

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. ΔH is negative.

Back

Preview of the back of card 3

Card 4

Front

The heat content that is stored in a chemical system.

Back

Preview of the back of card 4

Card 5

Front

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard state. ΔcHΘ

Back

Preview of the back of card 5
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