# Year one energetics

Define enthalpy change
Heat is the hear energy transferred in a reaction at constant pressure
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What is the symbol for enthalpy and the units?
delta H and KJ mol-1
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What are the standard conditions for enthalpy?
100KPa, 298K and all concentrations are 1 molar
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Define exothermic
Reactions that give out heat, ∆H is negative
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Define endothermic
Reactions that absorb energy, ∆H is positive
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What type of reaction occurs when you break bonds?
You need energy to break bonds, so bond breaking is endothermic
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What type of reaction occurs when you form bonds?
Energy is released when bonds are formed, so bond making is exothermic
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Define bond enthalpy
Energy required to break a certain amount of bonds, always will be ∆
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Why are book data values for enthalpy different from actual?
Book values use mean bond enthalpies
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State the calorimetry equation
q = m x c x delta T, q= enthalpy change, m= mass of water g, c= 4.18, delta T= temp change in K
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State Hess' law
The total enthalpy change of a reaction is independent to the route taken
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Define standard enthalpy of formation
When 1 mole of a compound is formed from its elements in their standard states under standard conditions
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Define standard enthalpy of combustion
When 1 mole of a substance is completely burned in oxygen under standard conditions
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## Other cards in this set

### Card 2

#### Front

What is the symbol for enthalpy and the units?

#### Back

delta H and KJ mol-1

### Card 3

#### Front

What are the standard conditions for enthalpy?

### Card 4

#### Front

Define exothermic

### Card 5

#### Front

Define endothermic