Enthalpy
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- Created by: AliceTori
- Created on: 11-04-17 17:51
What is Enthalpy?
The heat content that is stored in a chemical system
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What is a chemical system?
The chemicals involved in the reaction
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What is the difference in enthalpy of reactants to products called?
Enthalpy change
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What does the law of the conservation of energy state?
That energy cannot be created or destroyed
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Where is heat energy transferred between in a chemical reaction?
The system and the surroundings
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What is meant by the term'universe'?
Everything involved in the reaction, system and surroundings
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How can enthalpy change be determined?
Experimentally by measuring the energy transfer between the system and the surroundings
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If the energy transfer is from the system to the surroundings, what type of change is it?
Exothermic change
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If the energy transfer is from the surroundings to the system, what type of change is it?
Endothermic change
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What does an enthalpy profile diagram show?
The relative enthalpies of reactants and products and the enthalpy change
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If a reaction is exothermic, where is the energy transferred from and to?
Energy is transferred from the system to the surroundings
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If a reaction is endothermic, where is the energy transferred from and to?
Energy is transferred from the surroundings to the system
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In an exothermic reaction the enthalpy change is ________ and what happens to the temperature of the surroundings?
Negative and the temperature of the surroundings increases
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In an endothermic reaction the enthalpy change is ________ and what happens to the temperature of the surroundings?
Positive and the temperature of the surroundings decreases
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What is meant by the term activation energy?
The minimum energy required to start a reaction by the breaking of bonds
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Reactions with a small activation energy take place rapidly, why?
Because the energy needed to break the bonds is readily available in the environment
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Reactions with a large activation energy take place very slowly or not at all, why?
Because there is such a large energy barrier that there is not enough energy readily available in the surroundings to start the reaction
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What is meant by the term standard conditions?
A pressure of 100 kPa, a stated temperature, usually 298 K (25 degree Celsius) and a concentration of 1 mol dm-3 (for reactions with aqueous solutions)
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What is meant by the term standard state?
The physical state of a substance under standard conditions
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What is meant by the term 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 in their standard states
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What is meant by the term standard enthalpy change of formation?
The enthalpy change that takes place when one mole of a compound is formed from its elements in their standard states under standard conditions
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When one mole of an element is formed from its elements, what enthalpy change value do the elements have?
0kJ per mol
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What is meant by the term 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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When a substance completely reacts with oxygen, it is said that the products are what?
The products are the oxides of the elements in the substance
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What is meant by the term standard enthalpy change of neutralisation?
The enthalpy change that accompanies a reaction of an acid by a base to form one mole of water, under standard conditions, with all reactants and products in their standard states
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What is meant by the therm standard enthalpy change of solution?
The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
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A standard solution is what?
A solution of known concentration
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What is meant by the term standard enthalpy change of atomisation?
The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state
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Why is the value of enthalpy change of neutralisation always the same?
Because a neutralisation reaction always involves the reaction of H+ (aq) ions and OH- (aq) ions to form one mole of water (H2O)
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Other cards in this set
Card 2
Front
What is a chemical system?
Back
The chemicals involved in the reaction
Card 3
Front
What is the difference in enthalpy of reactants to products called?
Back
Card 4
Front
What does the law of the conservation of energy state?
Back
Card 5
Front
Where is heat energy transferred between in a chemical reaction?
Back
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