Energetics

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What type of reaction gives out heat?
Exothermic
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Example of an exothermic reaction?
Neutralisation
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What type of reaction takes in heat?
Endothermic
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Example of an endothermic reaction?
Thermal Decomposition
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What is enthalpy change?
Measure a heat change at a constant pressure
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What are the standard conditions for measuring enthalpy change?
Pressure of 100kPa, temperature of 298K
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Why is the enthalpy change sign negative in a exothermic reaction?
Products end up with less energy than the reactants because they have lost energy when they heat up the surroundings
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Why is the enthalpy change sign positive in a endothermic reaction?
Products end up with more energy than the starting materials
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Why is it important to have standard pressure for enthalpy change?
Pressure affects the amount of heat given out by a reaction that involves gases.If a gas is given out some energy has to be used to push away the atmosphere, meaning less energy is given out as heat by a reaction
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What is standard molar enthalpy of formation?
Is the enthalpy change when 1 mole of compound is formed from its constituent elements under standard conditions, all reactants and products in standard states
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What is the standard molar enthalpy of combustion?
Is the enthalpy change when 1 mole of compound is completely burned in oxygen under standard conditions, all reactants and products in standard states
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What is temperature?
Average kinetic energy of particles in a system
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What is heat?
Measure of total energy of all particles present
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What is the equation for enthalpy change?
Mass of substance x SHC x temperature change
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What apparatus is used to measure enthalpy change?
Calorimeter
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What features does the flame calorimeter have to prevent further heatloss?
Enclosed flame, spiral chimney made of copper, fuel burns in PURE OXYGEN rather than air
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Why are polystyrene cups used for measuring enthalpy change?
Good insulators, and due to there low specific heat capacity
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What is Hess's Law?
The enthalpy change for a chemical reaction is the same, what ever route is taken from reactants to products
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What are the enthalpies of all elements?
0
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What happens to bonds in an endothermic reaction?
Broken
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What happens to bonds in an exothermic reaction?
Formed
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What is bond dissociation enthalpy?
Enthalpy change required to break a covalent bond with all speices in the gaseous state
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Other cards in this set

Card 2

Front

Example of an exothermic reaction?

Back

Neutralisation

Card 3

Front

What type of reaction takes in heat?

Back

Preview of the front of card 3

Card 4

Front

Example of an endothermic reaction?

Back

Preview of the front of card 4

Card 5

Front

What is enthalpy change?

Back

Preview of the front of card 5
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