Chemistry Definitions: F322, Module 3

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Enthalpy, H
The heat content that is stored in a chemical reaction
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Exothermic
Refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, heat is lost to the surroundings. ΔH = -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, heat is taken in from the surroundings. ΔH = +ve
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Enthalpy Profile Diagram
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 by the breaking of bonds
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Standard Conditions
Pressure of 100 kPa (1 atmosphere), temperature of 298 K (25°c) and a concentration of 1.0 mol dm-3
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Standard State
The physical state of a substance under the standard conditions of 100 kPa, 298 K and 1.0 mol dm-3
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Standard Enthalpy Change of Reaction, ΔHr°
The ΔH that accompanies a reaction in the molar quantities expressed in an equation under standard conditions with all reactants and products under their standard states
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Standard Enthalpy Chance of Combustion, ΔHc°
The ΔH that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products under their standard states
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Standard Enthalpy Change of Formation, ΔHf°
The ΔH that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
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Specific Heat Capacity, c
The energy required to raise the temperature of 1g of s substance by 1°c
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Bond Enthalpy
The enthalpy change that takes place when breaking, by homolytic fission, 1 mol of a given bond in the molecules of a given species
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Average Bond Enthalpy
The average enthalpy change that takes place when breaking, by homolytic fission, 1 mol of a given bond in the molecules of a given species
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Hess' Law
States that, 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
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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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Rate of Reaction
The change in concentration of a product or reactant in a given time
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Heterogeneous Catalysis
Catalysis of a reaction in which the catalyst has a different physical state from the reactants. Reactants are usually gases whilst the catalyst is a solid
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Homogeneous Catalysis
Catalysis of a reaction in which the the catalyst has the same physical state as the reactants, usually the (aq) or (g) state
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The Boltzmann Distribution
The distribution of energies of molecules at a particular temperature, often shown as a graph
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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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Dynamic Equilibrium
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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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, heat is lost to the surroundings. ΔH = -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, heat is taken in from the surroundings. ΔH = +ve

Back

Preview of the back of card 3

Card 4

Front

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 by the breaking of bonds

Back

Preview of the back of card 5
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