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C4- ENERGETICS > 4.3- MEASURING ENTHALPY CHANGES > Flashcards

4.3- MEASURING ENTHALPY CHANGES Flashcards

1
Q

What is the general name for the enthalpy change for any reaction?

A

standard molar enthalpy change of reaction ΔH°

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2
Q

What is standard molar enthalpy change of reaction ΔH° measured in?

A

kilojoules per mole kJmol-1

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3
Q

What is the standard molar enthalpy of formation ΔfH°?

A

enthalpy change when one mole of substance formed from its constituent elements under standard conditions, all reactants + products being in their standard states

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4
Q

What is the standard molar enthalpy of combustion ΔcH°?

A

enthalpy change when one mole of substance completely burnt in oxygen under standard conditions, all reactants + products being in their standard states

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5
Q

What is temperature related to?

A

average kinetic energy of particles in system

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6
Q

What happens to average KE and temperature as particles move faster?

A

average KE increases + temp goes up

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7
Q

Does the number of particles present affect temperature?

A

no

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8
Q

What is temperature measured with?

A

thermometer

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9
Q

What is heat a measure of?

A

total energy of all particles present in given amount of substance

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10
Q

What does heat depend on?

A

how much of substance present

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11
Q

What is included in the measure of heat?

A

energy of every particle

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12
Q

Where does heat flow from?

A

always flows from high to low temp

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13
Q

What is the enthalpy change of a reaction?

A

heat given out / taken in as reaction proceeds

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14
Q

Is there an instrument to measure heat directly?

A

no

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15
Q

How can you measure the enthalpy change?

A

arrange for heat to be transferred into particular mass of substance, often water

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16
Q

What three things do you need to know when trying to work out enthalpy change?

A

mass of substance that’s being heated up/cooled down
temp change
specific heat capacity of substance

17
Q

What is specific heat capacity?

A

amount of heat needed to raise temperature of 1g of substance by 1K

18
Q

What is the units for specific heat capacity?

A

Jg-1K-1

19
Q

Enthalpy change equation

A

q = mcΔT

20
Q

How is a simple calorimeter used?

A

burn fuel to heat known mass of water + then measure temp rise of water
assume all heat from fuel goes into water

21
Q

What can the simple calorimeter be used to compare?

A

ΔcH° values of series of similar compounds as errors will be similar for every experiment

22
Q

Is the flame calorimeter better than the simple calorimeter?

A

yes

23
Q

Why is the flame calorimeter better than the simple calorimeter?

A

designed to reduce heat loss even further

24
Q

How is the flame calorimeter designed to reduce heat loss even further than the simple calorimeter? (3)

A

spiral chimney made of copper
flame enclosed
fuel burns in pure oxygen, rather than air

25
Q

How easy is it to measure heat changes for reactions that take place in reactions?

A

relatively easy

26
Q

How is the heat generated in solutions?

A

by themselves + only has to be kept in calorimeter

27
Q

What is often used for the calorimeters? (measuring enthalpy change of reactions in solutions)

A

expanded polystyrene

28
Q

What are expanded polystyrene good at?

A

good insulators

29
Q

As expanded polystyrene is a good insulator what do they do?

A

reduce heat loss through their sides

30
Q

What does expanded polystyrene have a low of?

A

low heat capacity

31
Q

What does it mean as expanded polystyrene has a low heat capacity?

A

absorb very little heat

32
Q

What is the specific heat capacity of dilute solutions usually taken to be?

A

same as water- 4.2Jg-1K-1

33
Q

What type of reactions are neutralisation reactions in solution?

A

exothermic- give out heat

34
Q

General equation for acid neutralised by alkali?

A

acid + alkali -> salt + water

35
Q

How do you find the enthalpy change for a reaction?

A

use quantities in moles given by balanced equation

36
Q

When will a metal displace another one from a compound?

A

when a metal is more reactive than another, it will displace the less reactive one from a compound

37
Q

If a metal that’s more reactive than another and displaces the less reactive one in a compound + compound can dissolve in water, how can the reaction be investigated?

A

using polystyrene beaker

38
Q

What will happen even if expanded polystyrene cups are good insulators?

A

some heat will still be lost from side + top leading to known values for enthalpy changes measured by this method

C4- ENERGETICS (7 decks)

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