Enthalpy and green chemistry key definitions

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Enthalpy, H
Heat energy stored in a chemical system.
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Exothermic
When enthalpy is smaller at the end of a reaction than at the beginning. Results in heat loss. Delta H -ive.
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Endothermic
When enthalpy is greater at the end of a reaction than at the beginning. Results in heat being taken in. Delta H +ive.
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Activation energy
Minimum energy required to start a reaction by the breaking of bonds.
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Enthalpy profile diagram
Shows the enthalpy of the reactants and products along with the activation energy and the enthalpy change.
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Standard conditions
Pressure of 100kpa and temperature of 298K (25 deg.celcius). In solution, concentration of 1M.
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Standard state
The state we find a substance in under standard conditions.
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Standard enthalpy change of reaction
The enthalpy change that accompanies the moles given in a balanced equation that are reacted under standard conditions and in standard states.
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Standard enthalpy change of combustion
Enthalpy chnage when one mol of reactant is burned completely in oxygen under standard conditions.
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Standard enthalpy change of formation
Enthalpy chnage when one mol of product is formed from its constituent elements in standard states under standard conditions.
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Specific heat capacity
Energy required to heat 1g of substance by 1K.
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Bond enthalpy
Enthalpy change when one mol of given bonds is broken by homolytic fission in a gaseous state.
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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 chnage for each route is the same.
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Rate of reaction
The change in concentration of reactant or product in a given time.
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Catalyst
A species that lowers the activation energy of a reaction by providing an alternate route but is not used itself.
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Boltzmann Distribution
Distribution of energies of molecules within a sample at a given temperature.
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Dynamic equlibrium
Equilibrium in a closed system where the rate of the forward reaction equals that of the reverse reaction leaving constant concentrations of reactants and products.
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Le Chatelier's principle
When change is imposed on a system in dynamic equilibrium the position of equilibrium will change to minimise the change.
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Greenhouse effect
The process by which absorption and subsequent emission of IR radiation by atmospheric gases warms the lower atmosphere and the earth's surface.
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Troposphere
Lowest layer of Earth's atmosphere to between 7km & 20km.
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Stratosphere
Second layer of atmosphere contains ozone layer. From troposphere to ~50km
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Adsorption
Process by which a gas, liquid or solute is held to a solid surface - such as in a catalytic convertor.
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Other cards in this set

Card 2

Front

When enthalpy is smaller at the end of a reaction than at the beginning. Results in heat loss. Delta H -ive.

Back

Exothermic

Card 3

Front

When enthalpy is greater at the end of a reaction than at the beginning. Results in heat being taken in. Delta H +ive.

Back

Preview of the back of card 3

Card 4

Front

Minimum energy required to start a reaction by the breaking of bonds.

Back

Preview of the back of card 4

Card 5

Front

Shows the enthalpy of the reactants and products along with the activation energy and the enthalpy change.

Back

Preview of the back of card 5
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