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Chemistry > AS.7 Enthalpy Changes > Flashcards

AS.7 Enthalpy Changes Flashcards

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1
Q

Enthalpy

A

Measure of heat of a system

H

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2
Q

Enthalpy change

A

Heat change of a chemical reaction associated with an equation

Triangle H

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3
Q

Exothermic

A

When heat is given from the system to the surroundings

“Release heat”

Chemical system loses energy so enthalpy change is negative

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4
Q

Endothermic

A

When heat is absorbed from the surroundings to the system

“Absorb heat”

Chemical system gains energy so enthalpy change is positive

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5
Q

Exothermic graph

A

Reactants are higher than products

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6
Q

Endothermic

A

Reactants are lower than products

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7
Q

Exothermic bonds

A

Energy released when making bonds is greater than energy required when breaking bonds

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8
Q

Endothermic bonds

A

Energy required when breaking bonds is greater than energy released when making bonds

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9
Q

Activation energy

A

The minimum amount of energy required for a reaction to occur

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10
Q

Drawing Ea on the graph

A

From reactants to activation energy

Arrow pointing up always

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11
Q

Drawing Ec on a graph

A

From reactants to lower activations energy

Arrow pointing up always

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12
Q

Drawing enthalpy change on a graph

A

Reactants to products

If up - endothermic

If down - Exothermic

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13
Q

Standard conditions for enthalpy

A

100kPa

298K

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14
Q

Enthalpy of combustion

A

The enthalpy change when one mole of a compound is burned completely in excess oxygen under standard conditions

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15
Q

Enthalpy of formation

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions

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16
Q

Enthalpy of neutralisation

A

The enthalpy change for the reaction of acid with base to produce one mole of water under standard conditions

17
Q

Measuring enthalpy changes

A

Calorimeter

18
Q

Calculation for enthalpy change

A

1) Q= mc ^T

2) -Q / n = ^H

19
Q

Average bond enthalpies

A

The energy required to break one mole of bonds in gaseous molecules

20
Q

Calculating bond enthalpies

A

^rH = bonds broken - bonds made

kJmol-1

21
Q

Hess law

A

The enthalpy change for a reaction is the same whichever route is taken from reactants to products

22
Q

Using enthalpy of combustion data for Hess law

A

If given combustion data, arrows point down

23
Q

Using enthalpy of formation data for Hess law

A

If given formation data, arrows point up

24
Q

Why are standard enthalpy changes of combustion less exothermic than expected when experimented

A

Energy lost as heat to surroundings

Non standard conditions

Incomplete combustion

Chemistry (27 decks)

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