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OCR A level Chemistry > Enthalpy change > Flashcards

Enthalpy change Flashcards

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1
Q

What symbol is used for the energy change of an exothermic reaction?

A

-

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2
Q

What symbol is used for the energy change of an endothermic reaction?

A

+

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3
Q

What is meant by enthalpy?

A

a measure of the heat energy in a chemical system

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4
Q

For an exothermic reaction what will happen to the temperature of the reaction mixture?

A

It will rise

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5
Q

For an endothermic reaction what will happen to the temperature of the reaction mixture?

A

It will fall

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6
Q

Why do most chemical reaction have an activation energy?

A

It is necessary to break bonds in reactant molecules

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7
Q

What is meant by a chemical system?

A

The atoms, molecules, or ions making up the chemicals

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8
Q

What is meant by the surroundings?

A

The apparatus, the laboratory (everything that isn’t the chemical system)

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9
Q

What directions can energy transfer occur in?

A
  • From the chemical system to the surroundings (exothermic)

- From the surroundings to the chemical system (endothermic)

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10
Q

What is the symbol for enthalpy?

A

H

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11
Q

What is the y axis on enthalpy profile diagrams?

A

enthalpy, H

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12
Q

What is the x axis on ethalpy profile diagrams?

A

Progress of the reaction

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13
Q

On an enthalpy profile diagram, for an exothermic reaction, what are the relative positions of the reactants and products?

A

The reactants are higher than the products

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14
Q

On an enthalpy profile diagram, for an endothermic reaction, what are the relative positions of the reactants and products?

A

The reactants are lower than the products

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15
Q

In terms of energy, how does bond breaking differ from bond making?

A

Bond breaking requires energy, whereas bond making releases energy

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16
Q

What is activation energy?

A

The minimum energy required for a reaction to take place

17
Q

What must be included when drawing an enthalpy profile diagram?

A

The following must be labelled:

  • reactants
  • products
  • enthalpy change (delta H)
  • activation energy
18
Q

What are the units for enthalpy change?

A

KJ per mol

19
Q

What are standard conditions?

A
  • 100KPa
  • 298k (25 degrees)
  • 1 mol per dm3 (applicable for solutions only)
20
Q

What are standard states?

A

The state of a substance under standard conditions

21
Q

What is the enthalpy change of formation?

A

The ENTHALPY change which accompanies the formation of one

mole of a substance from its elements under standard conditions with all reactants and products in their standard states

22
Q

What is the enthalpy change of combustion?

A

The enthalpy change which accompanies the complete combustion of one mole of a substance in oxygen, under standard conditions with all reactants and products in their standard states

23
Q

What is the enthalpy of formation of elements?

A

0 KJ per mole

24
Q

What is the enthalpy change of neutralisation?

A

The enthalpy change which accompanies the reaction of an acid BY a base to form one mole of water under standard conditions, with all reactants and products in their standard states.

25
Q

What must you remember when writing the answer for enthalpy change?

A
  • SIGN, - or +
  • UNITS KJ per mole or J per mole, check if the questions specifies
  • SIG FIGS, has the question specified?
26
Q

How do you convert from celcius to kelvin?

A

+273

27
Q

How do you determine the mass used in the energy change calculation?

A

It is the mass of the materials changing temperature

28
Q

What is the equation for energy change?

A

q=mc x temperature change

29
Q

What is q measured in?

A

J or KJ

30
Q

What does m represent in the energy change calculation?

A

Mass

31
Q

What does c represent in the energy change calculation?

A

Specific heat capacity of the material whose tempreature is being measured

32
Q

What is specific heat capacity?

A

The amount of energy required to raise the temperature of 1kg if a material by 1K

33
Q

What is k the unit for?

A

Kelvin

34
Q

How is temperature change in the energy change calculation worked out?

A

final temperature- initial temperature

OCR A level Chemistry (30 decks)

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