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Chemistry Module 3 > 3.2.1 Enthalpy Changes > Flashcards

3.2.1 Enthalpy Changes Flashcards

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1
Q

What is enthalpy?

A

Heat change in a reaction under standard conditions

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2
Q

What are standard conditions⦵?

A

100kPa

298K

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3
Q

Endothermic: +/- ΔH?

A

+

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4
Q

Exothermic: +/- ΔH?

A

-

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5
Q

Standard enthalpy change of reaction? ΔHr⦵

A

ΔH of a reaction under ⦵

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6
Q

Standard enthalpy change of formation? ΔHf⦵

A

ΔH when 1 mole of a compound formed from its elements in their standard states, under ⦵

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7
Q

Standard enthalpy change of neutralisation? ΔHn⦵

A

ΔH when an acid and alkali react to form 1 mole of water, under ⦵

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8
Q

Standard enthalpy change of combustion? ΔHc⦵

A

ΔH when 1 mole of a substance is completely burned in 02 to make CO2 and H20, under ⦵

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9
Q

Bond broken, exo or endo?

A

Endothermic

(BENDO)MEX

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10
Q

Bond made, exo or endo?

A

Exothermic

BENDO(MEX)

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11
Q

What is mean bond enthalpy?

A

Mean average to make/ break a bond

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12
Q

Why do we have mean bond enthalpies?

A

Because each bond has a slightly different enthalpy; easier

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13
Q

How do you calc. enthalpy change?

A

Total energy to break bonds – Total energy released from forming bonds

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14
Q

What is calorimetry?

A

Practical technique; work out enthalpy of combustion/ neutralisation

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15
Q

How can a calorimetry experiment give you the enthalpy change of a fuel?

A

q of calorimetry (kJ) / moles of fuel

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16
Q

What is the equation for calorimetry?

A 
q = mcΔT
q = energy (J)
m = mass of solution (g)
c = SHC of water (4.18)
ΔT = Δ in temp (K)
17
Q

How can a calorimetry experiment give you the enthalpy change of a neutralisation?

A

q of calorimetry (kJ) / moles of acid or base

18
Q

What is Bond dissociation enthalpy/ Average bond enthalpy?

A

Energy required to break the bonds in 1 mole of gas

19
Q

What is Hess’ law?

A

Total enthalpy change of reaction is independent of the route taken

20
Q

What 2 Hess cycles do you need to know?

A

Formation & combustion

21
Q

In a Hess cycle what do you do if you go against the arrows?

A

Reverse the +/- sign of the ΔH

22
Q

How do you check your Hess cycle is right?

A

Do a complete cycle = 0

23
Q

In a Hess cycle do you multiply the ΔH by the number of moles? E.g. 2O2

A

Yes

24
Q

What is the unit for enthalpy change?

A

kJmol-1

25
Q

What are the 4 types of enthalpy changes you need to know?

A

Standard enthalpy change of:

  1. Reaction
  2. Formation
  3. Neutralisation
  4. Combustion

Chemistry Module 3 (7 decks)

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