OCR Chemistry - Module 3 Energy

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  • Created by: Denise24
  • Created on: 12-03-14 12:00
Enthalpy
H, the heat content that is stored in a chemical system
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Exothermic
refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (deltaH is -ve)
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Endothermic
refers to 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 (deltaH is +ve)
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An Enthalpy profile diagram
is a diagram for a reaction to compare the enthalpy of the reactant with the enthalpy of the products
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Activation energy
is the minimum energy required to stat a reaction by the breaking of bonds
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Standard conditions
a pressure of 100kPa (1atmosphere), a stated temperature, usually 298K (25 degrees) and a concentration of 1.0 mol/dm cubed (for reaction with aqueous solutions)
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Standard state
Is the physical state of a substance under the standard conditions of 100kPa (1 atmospher) and 298K (25 degrees)
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Standard enthalpy change of combustion
The enthalpy change when 1 mol of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states
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Standard enthalpy change of formation
The enthalpy change when 1 mol of a compound is made from its constituent elements in their standard states, under standard conditions
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Specific heat capacity
c, is the energy required to raise the temperature of 1 g of a substance by 1 degrees
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Bond enthalpy
Is the enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species
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Average bond enthalpy
is the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species
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Hess' Law
If a reaction can take place by more than one route, intitial and final conditions are the same, the total enthalpy change is the same for each route
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An enthalpy cycle
is 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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Catalyst
Lowers the activation energy of a reaction by providing an alternative route for the reaction to follow
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Heterogeneous catalysis
is the catalysis of a reaction in which the catalyst has a different physical state from the reactants; frequently, reactants are gases whilst the catalyst is a solid
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Homogeneous catalysis
is catalysis of a reaction in which the catalyst and the reactants are in the same physical state, which is most frequently the aqeous or gaseous state
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Dynamic equilibrium
is the equilibrium that exists in a closed systemwhen the rate of the forward reaction is equal to the rate of the reverse reaction
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le Chatelier's principle
states that when a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change
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Other cards in this set

Card 2

Front

refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (deltaH is -ve)

Back

Exothermic

Card 3

Front

refers to 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 (deltaH is +ve)

Back

Preview of the back of card 3

Card 4

Front

is a diagram for a reaction to compare the enthalpy of the reactant with the enthalpy of the products

Back

Preview of the back of card 4

Card 5

Front

is the minimum energy required to stat a reaction by the breaking of bonds

Back

Preview of the back of card 5
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