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AS Chemistry > Energetics > Flashcards

Energetics Flashcards

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1
Q

What is enthalpy?

A

A measure of the heat content of a substance

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2
Q

What letter represents enthalpy?

A

H

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3
Q

What is enthalpy change?

A

The heat energy transferred in a reaction at a constant pressure in kJmol-1

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4
Q

What is enthalpy change represented by?

A

Delta H

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5
Q

What are standard conditions?

A

100kPa and a given temperature

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6
Q

What is the delta H value for exothermic reactions and why?

A

Negative because energy is given out to the surroundings

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7
Q

What is the delta H value for exothermic reactions and why?

A

Positive because energy is being absorbed by the surroundings

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8
Q

What is a reaction profile?

A

A diagram of enthalpy levels of the reactants and products in a chemical reaction.

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9
Q

What is the activation energy with reference to the reaction pathway?

A

The minimum input of energy required by reaction pathways to break the bonds in the reactants.

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10
Q

Where is the activation on an energy profile diagram?

A

The peak of the pathway

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11
Q

What is bond enthalpy?

A

The energy needed to break a bond

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12
Q

Is breaking bonds endo or exo?

A

Endothermic

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13
Q

Is making bonds endo or exo?

A

Exothermic

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14
Q

What is the mean bond enthalpy?

A

The average energy needed to break a bond over a range of compounds

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15
Q

What is the equation to calculate enthalpy change of reaction?

A

Total energy absorbed - total energy released

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16
Q

What are standard enthalpy values?

A

The delta H values for enthalpy changes of specific reactions measured under standard conditions

17
Q

What is the standard enthalpy of formation?

A

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

18
Q

What is the standard enthalpy change of combustion?

A

The enthalpy change when 1 mole of a substance is burned completely in oxygen under standard conditions while all the reactants and products are in their standard states

19
Q

What is the standard enthalpy change of reaction?

A

The enthalpy change of a reaction when it occurs in the molar quantities shown in the equation under standard conditions with all the reactants and products in their standard state

20
Q

What is a calorimetry experiment?

A

Experiments which measure the heat given out by reactions

21
Q

Describe how to conduct a calorimetry experiment for reactants in solution?

A

Dump reactants in a polystyrene cup, mix them and then measure the temp. change with a thermometer

22
Q

What is the enthalpy change of neutralisation?

A

The energy change when one mole of water is formed by the reaction of an acid and alkali

23
Q

What are the problems with calorimetry in general?

A

Heat absorbed by container, heat lost to surroundings

24
Q

What are the problems for flammable liquid calorimetry?

A

Some incomplete combustion so less energy given out

Some flammable liquid may evaporate

25
Q

What does Hess’s Law state?

A

The total enthalpy change for a reaction is independent of the route taken

26
Q

How do you calculate enthalpy change?

A

Enthalpy of products - enthalpy of reactants

27
Q

What are some examples of exothermic reactions?

A

Combustion and respiration

28
Q

What are some examples of endothermic reactions?

A

Photosynthesis and thermal decomposition

29
Q

What is the enthalpy change of reaction?

A

The enthalpy change associated with a stated reaction

30
Q

What is the enthalpy change of combustion?

A

The enthalpy change when one mole of a substance undergoes complete combustion

31
Q

What is enthalpy change of formation?

A

When one mole of a substance is formed from its elements

AS Chemistry (14 decks)

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