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15 Cards in this Set
- Front
- Back
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What is enthalpy? |
The measure of heat in a system |
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System -> surroundings |
Exothermic |
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Surroundings -> system |
Endothermic |
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Negative enthalpy change |
•exothermic •surroundings get hotter •arrow must point down •reactants have more energy than products •system loses energy |
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Positive enthalpy change |
•endothermic •surroundings get colder •arrow must point up •system gains energy •products have more energy than the reactants |
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Exothermic |
Energy released when making bonds is greater than the energy required when breaking bonds |
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Endothermic |
Energy required when breaking bonds is greater than energy released when making bonds |
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Standard conditions |
100kPa 298K (25°C) |
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Enthalpy of combustion |
The enthalpy change when one mole of a compound is burned completely in excess oxygen under standard conditions |
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Enthalpy of formation |
The enthalpy change when one mole of a compound is formed from its elements under standard conditions |
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Enthalpy of neutralisation |
The enthalpy change for the reaction of acid with base to produce 1 mole of water under standard conditions |
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Direct method of measuring enthalpy change |
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Indirect method of measuring enthalpy change |
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Q(J) = |
m c ∆T m c ∆Tm = mass of water(indirect)/aq solution in g(direct) c = 4.18 JK-¹g-¹ |
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∆H (JK-¹g-¹) = |
-Q / n (of one reactant) |
