UNIT 2 OCR CHEMISTRY ENERGY TOPIC

  • Created by: carys ☺
  • Created on: 28-04-13 19:20
What is enthalpy?
the heat content that is stored in a chemical system
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Define exothermic
Refers to a reaction in which the enthalpy change of the products is smaller than the enthalpy change of the reactants, resulting in heat loss to the surroundings (/\ -ve)
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What are examples of exothermic reactions?
oxidation of fuels and respiration
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What are examples of endothermic reactions?
thermal decomposition of limestone and photosynthesis
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What is the activation energy of a reaction?
The minimum energy required to start a reaction by the breaking of bonds
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What are the standard conditions?
A pressure of 100kPa (1 atmosphere), A stated temperature (-298K/25 degrees) and a concentration of 1 mol dm-3
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What is the standard enthalpy change of reaction?
the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states
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What is the 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 in their standard states
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What is the enthalpy change of formation?
is the enthalpy change when one mole of a compound is formed from its consituent elements in their standard states under standard conditions
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What is bond enthalpy?
the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bong in the molecules of a gaseous species
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State Hess' Law
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthapy change is the same for each route.
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What factors alter the rate of a chemical reaction?
temperature, pressure, concentration, surface area, adding a catalyst
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State le Chatelier's principle
When a system in dynamic equilibrium is subject to a change, the position of equilibrium will shift to minimise the change
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How does concentration effect equilibrium?
the equilibrium moves to the side without the species,, reducing its concentration
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How does pressure effect equilibrium?
the equilibrium moves to the side with fewer gaseous moles, reducing pressure
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How does temperature effect equilibrium?
the equilibrium moves in the endothermic direction, taking in the extra energy
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Other cards in this set

Card 2

Front

Define exothermic

Back

Refers to a reaction in which the enthalpy change of the products is smaller than the enthalpy change of the reactants, resulting in heat loss to the surroundings (/\ -ve)

Card 3

Front

What are examples of exothermic reactions?

Back

Preview of the front of card 3

Card 4

Front

What are examples of endothermic reactions?

Back

Preview of the front of card 4

Card 5

Front

What is the activation energy of a reaction?

Back

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