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AS Organic Chemistry > 9 Enthalpy Changes > Flashcards

9 Enthalpy Changes Flashcards

1
Q

What does ΔrH stand for?

A

enthalpy change of reaction

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2
Q

What is the enthalpy change of formation (ΔfH)?

A

the enthalpy change when one mole of a substance is formed from elements

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3
Q

Is a reaction exothermic or endothermic if ΔH is negative?

A

exothermic

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4
Q

If energy is released during a reaction is it endothermic or exothermic?

A

exothermic

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5
Q

When can Hess’ law be applied?

A

when the enthalpy change can not be measured directly

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6
Q

What is the equation for determining the energy release that can be measured by a calorimeter?

A

q = mcΔT

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7
Q

Is a reaction exothermic or endothermic if ΔH is positive?

A

Endothermic

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8
Q

How can the estimated temperature change immediately after mixing two liquids be found?

A

extrapolate a graph backwards

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9
Q

What is activation energy?

A

the minimum value of energy needed to break the required bonds and start the reaction

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10
Q

How can inaccuracies in a calorimeter be reduced?

A

reduce energy loss/ensure complete combustion

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11
Q

What is the enthalpy change of combustion (ΔcH)?

A

the enthalpy change when one mole of a substance is burnt completely in oxygen

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12
Q

What are standard conditions in a reaction?

A

100 kPa and a stated temperature

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13
Q

What is the symbol for enthalpy change of neutralisation?

A

ΔneutH

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14
Q

What units is enthalpy measured in?

A

kJ mol−1

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15
Q

What is Hess’ law?

A

the start and end of a reaction are important but not the route taken to get there

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16
Q

Is a reaction endothermic or exothermic if energy is taken in during the reaction?

A

endothermic

17
Q

What is needed to break bonds in molecules?

A

energy needs to be taken in

18
Q

What is specific heat capacity?

A

the amount of energy needed to increase the temperature of 1 g of a substance by 1 K

19
Q

How is the enthalpy change in a reaction calculated?

A

calorimetry/Hess’ law/difference between energy released by bond formation and energy taken in by breaking bonds

20
Q

What is the standard enthalpy of formation (ΔfH⦵)?

A

the enthalpy change when one mole of a substance is formed from elements (in their standard states) under standard conditions

AS Organic Chemistry (8 decks)

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