Enthalpy Key Definitions

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Enthalpy
H- heat content that is stored in chemical reaction
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Exothermic
Enthalpy of the products is smaller than the enthalpy of the reactants- heat loss to the surroundings (-deltaH)
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Endothermic
Enthalpy of the products is greater than the enthalpy of the reactants- heat taken in from the surroundings (+deltaH)
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Enthalpy Profile
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products
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Activation Energy
The minimum energy required to start a reaction (breaking of bonds)
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Standard Conditions
Pressure- 100kPa (1 atmosphere), Temperature- 298K (25°C) -1.0 moldm-3 solutions where solutions are involved
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Standard State
The physical state of a substance under the standard conditions
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The Standard Enthalpy of a Reaction
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions
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The Standard Enthalpy Change of Neutralisation
The enthalpy change when 1 mole of water is is formed from reaction between an acid and an alkali, under standard conditions
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The Standard Enthalpy Change of Combustion
The enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions
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The Standard Enthalpy Change of Formation
The enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states
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Specific Heat Capacity
C, the energy required to raise the temperature of 1g of a substance by 1°C
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Bond Enthalpy
The enthalpy change that takes place when breaking, by homolytic fission, 1 mole of a given bond in gaseous molecules
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Average Bond Enthalpy
The average enthalpy change when breaking, by homolytic fission, 1 mole of a given type of bond in gaseous molecules
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Hess' Law
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
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Enthalpy Cycle
A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess' Law
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Card 2

Front

Enthalpy of the products is smaller than the enthalpy of the reactants- heat loss to the surroundings (-deltaH)

Back

Exothermic

Card 3

Front

Enthalpy of the products is greater than the enthalpy of the reactants- heat taken in from the surroundings (+deltaH)

Back

Preview of the back of card 3

Card 4

Front

A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products

Back

Preview of the back of card 4

Card 5

Front

The minimum energy required to start a reaction (breaking of bonds)

Back

Preview of the back of card 5
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