Special form of potential energy that lies within chemicsl bonds
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Chemical Bonds
Forces of attraction that bind together atoms in compounds
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Enthalpy, H
The thermal energy stored in a chemical system
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System
The actual chemical reaction-the atoms and bonds involved
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Surroudings
Everything else, including the aqueous solution that substances are dissolved in
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Conservation of energy law
Energy cannot be created or destroyed, only transferred from one place to another
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Enthalpy change, delta H
The heat exchanged with the surroundings during a chemical reaction, at constant pressure. The difference between the enthalpy of the products and the enthalpy of the reactants= Hproducts-Hreactants
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Exothermic Reaction (negative)
Heat is lost from the chemical system to the surroundings. The enthalpy of products is smaller than the enthalpy of the reactants
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Endothermic Reaction (positive)
There is heat gain to the chemical system from the surroundings. The enthalpy of the products is greater than the enthalpy of the reactants
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Activation Energy
The minimum energy required to start a reaction by breaking bonds in the reactants. Stops reactions from taking place spontaneously. Can be shown in enthalpy profile diagrams
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Thermodynamics
Branch of chemistry that focuses on energy in a chemical system, which is the reactants and products
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Standard conditions
100kPa and 298 Kelvins
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Enthalpy Change of a reaction
The energy change associated with a given reaction
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Enthalpy change of formation
The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions
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Enthalpy change of combustion
The energy change that occurs wjen 1 mole of a substance is completely combusted
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Enthalpy change of neutralisation
The energy change associated with the formation of 1 mole of water from a neutralisation reaction
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Calorimetry
The quantitative study of energy in a chemical reaction. You can't measure enthalpy directly but you can measuring enthalpy change by monitoring the temperature and using q=mc(delta)t
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Specific heat capacity
Energy required to raise the temperature of 1g of a substance by 1k
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Bomb Calorimeter
Sophisticated piece of equipment that minimises hear loss as much as possible and uses pure oxygen to ensure complete combustion is achieved
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Average bond enthalpy
The mean energy needed when breaking, by homolytic fission, 1 mole of a given type of bond in gaseous molecules
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Hess' Law
The enthalpy change in a chemical reaction is independent of the route it takes
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Enthalpy cycle
A pictorial representation showing alternative routes between reactants and products
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Catalyst
A substance that increases the rate of reaction without being used up during the process. It lowers the activation energy by providing an alternative route for the reaction to follow.
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Homogenous Catalyst
Catalyst in the same phase as the reactants eg. liquid catalyst and liquid reactants
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Heterogenous Catalyst
Catalyst in a different phases from the reactants eg. solid catalyst and gaseous/liquid reactants or if all chemicals are immiscible and the catalyst is in a different liquid layer to the reactants
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Boltzman distribution
The distribution of energies of molecules at a particular temperature, often shown as a graph
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Dynamic equilibrium
Nothing appears to be happening at equilibrium but the system is in constant motion. The rate of the forward reaction=the rate of the backward reaction. The concentrations of the reactants and products remain constant.System must be isolated.
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Position of equilibrium
The extent of a reaction. Equilibrium not established until the reaction has been occurring for a period of time
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Le Chatelier's Principle
When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to minimise the change
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Equilibrium Constant, Kc
Considers the postion of an equilibrium, giving a measure of where the equilibrium lies by essentially giving the ratio between products and reactants. Kc=products/reactants
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Equilibrium Law
Tells us that if reactants A and B and products C and D are in the equilibrium: aA+bB->cC+dD then they are related by the Kc expression.
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Other cards in this set
Card 2
Front
Forces of attraction that bind together atoms in compounds
Back
Chemical Bonds
Card 3
Front
The thermal energy stored in a chemical system
Back
Card 4
Front
The actual chemical reaction-the atoms and bonds involved
Back
Card 5
Front
Everything else, including the aqueous solution that substances are dissolved in
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