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Edexcel A Level Chemistry > ✅8 - Energetics I > Flashcards

✅8 - Energetics I Flashcards

1
Q

What is enthalpy change?

A

The heat energy change in a reaction at constant pressure

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2
Q

What are the units for enthalpy change?

A

kJmol-1

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3
Q

What are the standard conditions?

A

Elements in their standard states
100kPa
298K

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4
Q

What are exothermic reactions?

A

Give out energy, negative enthalpy change

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5
Q

What are endothermic reactions?

A

Take in energy, positive enthalpy change

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6
Q

What do enthalpy level diagrams show?

A

Overall relative change in a reaction

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7
Q

What does an enthalpy level diagram look like for an exothermic reaction?

A

Reactants higher than products

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8
Q

What does an enthalpy level diagram look like for an endothermic reaction?

A

Products higher than reactants

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9
Q

What do reaction profile diagrams show?

A

Enthalpy changes during a reaction

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10
Q

What is the activation energy?

A

The minimum energy needed for the reaction to occur

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11
Q

Why are standard conditions important?

A

Changes in temperature and pressure can affect enthalpy

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12
Q

What is the standard enthalpy change of reaction?

A

The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation under standard conditions

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13
Q

What is the standard enthalpy change of formation?

A

The enthalpy change when one mole of a product is formed from its constituent elements in their standard states under standard conditions

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14
Q

What is the standard enthalpy change of combustion?

A

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

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15
Q

What is the standard enthalpy change of neutralisation?

A

The enthalpy change when an acid and an alkali react to form one mole of water under standard conditions

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16
Q

How would you calculate an enthalpy change?

A

Mass of solution heated x specific heat capacity of solution x temperature change

17
Q

What is Hess’ Law?

A

The total enthalpy change of a reaction is always the same, no matter which route is taken

18
Q

What is the enthalpy change of formation for elements?

A

Zero

19
Q

How can the enthalpy changes of reaction be worked out from enthalpy changes of formation?

A

Using the formation of the reactants and products, and the enthalpy change of reaction on top

20
Q

How can enthalpy changes be worked out from enthalpy of combustion?

A

By using the combustion of both reactants and products and putting the unknown on top

21
Q

How can indirect enthalpy changes be found?

A

By doing the required experiments and then using Hess’ Law

22
Q

Bond breaking is…

A

…endothermic

23
Q

Bond making is…

A

…exothermic

24
Q

What is bond enthalpy?

A

The energy needed to break q mole of a type of bond in a molecule in the gas phase

25
Q

How are mean bond enthalpies calculated?

A

By taking an average of all the different values fr a bond type

26
Q

How can enthalpy changes be worked out from bond enthalpies?

A

Sum of bond enthalpies of reactants - sum of bond enthalpies of proudcts

Edexcel A Level Chemistry (20 decks)

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