Energy

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Undergraduate Chemistry - Part 2 (Energy) Flashcards on Energy, created by siobhan.quirk on 24/05/2013.
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Flashcards by siobhan.quirk, updated more than 1 year ago
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Question Answer
Enthalpy the heat content that is stored in a chemical systen
Exothermic a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (-ve)
Endothermic a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting is heat being taken in from the surroundings (+ve)
Enthalpy profile diagram is a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products
Activation energy the minimum energy required to start a reaction by the breaking of bonds
Standard conditions a pressure of 100kPa, a stated temperature usually 298K and a concentration of 1.0moldm-3
Standard state physical state of a substance under standard conditions of 100kPa and 298K
Standard enthalpy change of combustion the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states
Standard enthalpy change of formation the enthalpy change that takes place when one mole of a compounds is formed from its constituent elements in their standard states under standard conditions
Specific heat capacity the energy required to raise the temperature of 1g of a substance by 1 degrees
Bond enthalpy enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species
Average bond enthalpy the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species
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
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
Rate of reaction the change in concentration of a reactant or product in a given time
Heterogenous catalysis catalysis of a reaction in which the catalyst has a different physical state from the reactants
Homogeneous catalysis catalysis of a reaction in which the catalysts and reactants are in the same physical state
Boltzmann Distribution distribution of energies of molecules at a particular temperature
Dynamic equilibrium the equilibrium that exists in a closed system when the rate of the forward reaction is euql to the rate of the reerse reaction
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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