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A Level Chemistry > Enthalpy > Flashcards

Enthalpy Flashcards

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1
Q

What is enthalpy?

A

Describes all of the heat energy in a single chemical system

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2
Q

Enthalpy symbol

A

H

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3
Q

What can we use to measure enthalpy with instead (because it is too difficult to find)?

A

Enthalpy change

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4
Q

Enthalpy change symbol

A

△H

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5
Q

Unit of enthalpy/enthalpy change

A

Joules (J)

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6
Q

Enthalpy change on a reaction profile diagram

A

The difference between the enthalpy of reactants to the enthalpy of the products

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7
Q

reaction profile diagram of exothermic reaction

A

The reactants are higher than products (reactants have higher enthalpy than products)
Because energy was given out

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8
Q

Enthalpy change of an exothermic reaction

A

The enthalpy of products (lower) take away reactants (higher)
This value is negative to show energy lost to surroundings

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9
Q

Reaction profile diagram of an endothermic reaction

A

The products have higher enthalpy than reactants to show energy gained by molecules

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10
Q

Enthalpy change of an endothermic reaction

A

Enthalpy of products (higher) take away reactants (lower)
So value is positive to show energy taken in from surroundings

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11
Q

Under what conditions are enthalpy changes measured in?

A

Standard conditions

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12
Q

Standard conditions

A

25°c temp
100 kPa
1molddm-3
All chemicals in their standard states (solid, liquid gas etc)

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13
Q

Standard enthalpy change symbol

A

△H⦵

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14
Q

Units for standard enthalpy change

A

KJmol-1
The enthalpy change (in energy, kilojoules) per MOL

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15
Q

Standard enthalpy change of combustion

A

The enthalpy change in a reaction when 1 mol of a substance reacts completely with oxygen (in complete combustion) under standard conditions where all species are in standard states

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16
Q

Standard enthalpy change of combustion symbol

A

△cH⦵

17
Q

Important about standard enthalpy change of combustion?

A

BALANCED AROUND 1 MOL OF SUBSTANCE COMBUSTING

18
Q

Balancing combustion questions?

A

Balance the C in co2 first so equal to the carbon amount in 1 mol of the substance being burnt
Then hydrogen in water to be equal to hydrogen in 1 mol of substance
Then oxygen

19
Q

Standard enthalpy change of neutralisation symbol

A

△neutH⦵

20
Q

Standard enthalpy change of neutralisation definition

A

The enthalpy change in a reaction when 1 mole of water is formed in a neutralisation reaction between an acid and an alkali under standard conditions when all species are in standard states

21
Q

What is important about standard enthalpy change of neutralisation ?
Equation

A

The equation is balanced around 1 mole of water always

22
Q

Standard enthalpy change of neutralisation values are always…

A

Always negative: neutralisation reactions are exothermic

23
Q

Standard enthalpy change of combustion values are always…

A

Always negative
Combustion reactions are exothermic

24
Q

Standard enthalpy change of neutralisation between a strong acid and strong alkali

A

Usually around 57kjmol-1 : string acids and alkalis fully ionise to H+ + OH- ——> H2O

25
Q

Standard enthalpy change of formation symbol

A

△fH⦵

26
Q

Standard enthalpy change of formation definition

A

The enthalpy change in a reaction when 1 mole of a COMPOUND is formed from its elements under standard conditions (where all species are in its standard states)

27
Q

What’s important about standard enthalpy change of formation equations?

A

Balanced around 1 mole of a compound
The elements are in its standard states: eg oxygen is O2, hydrogen is H2, halogens etc

28
Q

Standard enthalpy change of reaction symbol

A

△rH⦵

29
Q

Standard enthalpy change of reaction definition

A

The enthalpy change in a reaction when a reaction takes place in the molar quantities shown in the BALANCED chemical equation under standard conditions in standard states

30
Q

When is standard enthalpy change of reaction used?

A

If the reaction is not neutralisation, combustion or formation
So for any other reaction

31
Q

When defining any enthalpy change of x, what must you specific?

A

The standard conditions such as:
298K
100 KPa
1 molddm-3
Standard states

32
Q

System

A

The atoms and bonds involved in a chemical reaction

33
Q

Law of conservation

A

Energy in a closed system will always remain the same, none can be created or destroyed
Only transferred from one form to another

A Level Chemistry (88 decks)

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