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A-Level Chemistry > Enthalpy changes > Flashcards

Enthalpy changes Flashcards

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1
Q

What is enthalpy?

A

A measure of the heat energy in a system

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2
Q

What is the equation for enthalpy change?

A

ΔH = H(products) - H(reactants)

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3
Q

What is the system?

A

The chemicals - the reactants and products

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4
Q

What is the surroundings?

A

The apparatus, the lab and everything that is not the system

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5
Q

What does exothermic mean?

A

The energy is transferred from the system to the surroundings - ΔH is negative

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6
Q

What does endothermic mean?

A

The energy is transferred from the surroundings to the system - ΔH is positive

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7
Q

What does the energy profile look like for an exothermic reaction?

A
  • The system releases heat energy to surroundings
  • Any energy loss by the chemical system is balanced by the same energy gain by by the surroundings
  • ΔH is negative
  • Temperature of the surroundings increases
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8
Q

What does the energy profile look like for an endothermic reaction?

A
  • The chemical system takes in energy from surroundings
  • Any energy gain by the system is balanced by the same energy loss by the surroundings
  • ΔH is positive
  • Temperature of the surroundings decreases
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9
Q

What is activation energy?

A

The minimum energy required for a reaction to take place

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10
Q

What does the enthalpy profile, including activation energy, look like for an exothermic reaction?

A
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11
Q

What does the enthalpy profile, including activation energy, look like for an endothermic reaction?

A
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12
Q

What is standard pressure?

A

100kPa

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13
Q

What is standard temperature?

A

298 K

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14
Q

What is standard concentration?

A

1 mol dm^-3

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15
Q

What is standard state?

A

The physical state of a substance under standard conditions

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16
Q

What is standard enthalpy change of reaction, Δr HΘ?

A

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, will all reactants and products in their standard states

17
Q

What is standard enthalpy change of formation, Δf HΘ?

A

The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

18
Q

What is standard enthalpy change of combustion?

A

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states

19
Q

What is standard enthalpy change of neutralisation?

A

The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions, with all reactants and products in their standard states

20
Q

What is the energy and specific heat capacity equation?

A

q = mcΔT

q= energy J
m = mass g
c = specific heat capacity J g^-1 K^-1
T = temperature K

21
Q

How do you determine the enthalpy change of combustion?

A
22
Q

How do you carry out the spirit burners experiment?

A
23
Q

How do you carry out the cooling curves/ polystyrene cup experiment?

A
24
Q

What is average bond enthalpy?

A

The energy required to break one mole of a specified type of bond in a gaseous molecule

25
Q

What are the rules of bond enthalpies?

A
  • They are always endothermic
  • They always have a positive value
26
Q

What in bond breaking?

A

Endothermic

27
Q

What is bond making?

A

Exothermic

28
Q

How can you find the enthalpy change of reaction using bond enthalpies?

A

Δr H = E (bond enthalpies in Reactant - E (bond enthalpies in Product_

29
Q

What is Hess’ law?

A

If a reaction can take place by 2 routes, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route

30
Q

How can Hess’ law be represented on an enthalpy profile?

A
31
Q

How can you find the enthalpy change of reaction from the enthalpy changes of formation?

A

Δr H = E (Δf H products) - E (Δf H reactants)

32
Q

How can you find the enthalpy change of reaction from the enthalpy changes of combustion?

A

Δr H = E(Δc H reactants) - E(Δc H products)

A-Level Chemistry (42 decks)

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