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Energy Module
Definitions
21
Chemistry
12th Grade
03/23/2012

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Term
Entahlpy change of formation
Definition
This is where one mole of product is formed from its constiuent elements in their standard states under standard conditions of 298K and 100KPa.
Term
Enthalpy change of combustion
Definition
The enthalpy change that takes place when one mole of a substance reacts fully with oxygen under standard conditions with all reactants and products in their standard states.
Term
Enthalpy change of reaction
Definition
The enthalpy change that goes with a reaction in the molar quantities under standard conditions with reactants and products in standard states
Term
Standard conditions
Definition
A pressure of 100KPa a stated temperature, usually 298K and a concentration of 1 mole per dm -3
Term
the Boltzmann Distibution
Definition
The distribution of energies of molecules at a particular temperature, usually shown as a graph
Term
Enthalpy
Definition
The heat content that is stored in a chemical system
Term
Exothermic
Definition
A reaction in which the enthalpy of products is smaller than that of the reactants, resulting in a heat loss
Term
Endothermic
Definition
A reaction in which the enthalpy of the products is greater than the enthalpy of reactants, resulting in a heat gain.
Term
Enthalpy profile diagram
Definition
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products
Term
Activation energy
Definition
The minimum energy required to start a reaction by the breaking of bonds
Term
Standard state
Definition
the physical state of a substance under the standard conditions, 298K and 100KPa
Term
Specific heat capacity
Definition
The energy required to raise the temperature of 1g of a substance by 1C
Term
Bond enthalpy
Definition
the enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecules of a gaseous species
Term
Average bond enthalpy
Definition
the average enthalpy change that takes place when breaking homolytic fission 1 mole of a given type of bond in the molecules of a gaseous species.
Term
Hess's Law
Definition
if a reaction can take place by more than one route and the intial and final conditions are the same, the total enthalpy change is the same for each route
Term
Enthalpy Cycle
Definition
a diagram showing alternative routes between reactants and products that allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess's Law
Term
Rate of reaction
Definition
the change in concentration of a reactant or product over time
Term
Heterogenous catalyst
Definition
a reaction in which the catalyst has a different physical state from the reactants; frequently, reactants are gases whilst the catalyst is a solid
Term
Homogeneous catalyst
Definition
a reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state
Term
le Chatelier's Principle
Definition
when a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change
Term
Dynamic equilbrium
Definition
the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction
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