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Chemistry (Tara) > Thermochemistry > Flashcards

Thermochemistry Flashcards

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1
Q

Heat of reaction

A

the heat change that occurs when a reaction takes place according to a given balanced equation

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2
Q

exothermic reaction

A

heat is given out from the reaction to the surroundings (-)

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3
Q

endothermic reaction

A

heat is taken in from the surroundings (+)

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4
Q

ΔH = -

A

exothermic

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5
Q

ΔH = +

A

endothermic

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6
Q

Heat of combustion

A

the heat change that occurs when 1 MOLE of a certain substance is burned in an excess of oxygen

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7
Q

unit of heat of combustion

A

Kj/mol

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8
Q

if the quantity is not a mole and you want to find the heat of combustion

A

adjust it (divide or multiply)

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9
Q

when you are finding the heat of combustion which side of the equation does the substance go?

A

left (it is a reactant)

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10
Q

what is the function of the bomb calorimeter 2

A

to accurately measure the heat of combustion or the kilogram calorific value

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11
Q

bomb calorimeter:

what holds the substance

A

the crucible

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12
Q

bomb calorimeter:

what heats it and ignites the sample

A

wires that can be electrically heated

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13
Q

bomb calorimeter:

what provides the excess of oxygen

A

an inlet tube

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14
Q

2 things found in the water in the bomb calorimeter and what are their functions

A

thermometer to measure the heat change and stirrer to get an accurate reading

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15
Q

5 things you need to know about a bomb calorimeter to do the calculation

A
  1. amount of substance burned
  2. initial and final temperature of water
  3. specific heat capacity of water
  4. the heat capacity of the calorimeter
  5. the mass of water in KG
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16
Q

what substances always have the same result

A

those with a definite formula

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17
Q

what substances always have different results

A

peat, coal etc. depends on their composition

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18
Q

Kilogram calorific value

A

the heat that is produced when 1kg of the fuel is burned in an excess of oxygen

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19
Q

units of Kilogram calorific value

A

KJ/Kg

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20
Q

Heat of formation

A

the heat change that occurs when 1 MOLE of a substances is formed from its elements in their standard states

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21
Q

unit of Heat of formation

A

KJ/mole

22
Q

where does the substance go in the equation when find the Heat of formation

A

on the left (it is a reactant)

23
Q

why is it more difficult to find the heats of formation rather than the heats of combustion

A

as other products along with the main product will be formed also

24
Q

Hess’ Law

A

if a chemical reaction takes place in several stages, then the sum of the individual stages equals the heat change if the reaction has been carried out in one single stage

25
Q

what is Hess’ law an example of

A

the law of conservation of energy

26
Q

The law of conservation of energy

A

energy cannot be created nor destroyed, it can only be converted from one form of energy to another

27
Q

heat of neutralisation of strong acids

A

-57 KJ/mol

28
Q

why are heats of neutralisation of strong acids all the same?

A

because essentially the same reaction is happening in all of them - the hydrogen ion from the acid reacts with the hydroxide ion from the base to form water

29
Q

heats of neutralisation of weak acids and explain

A

less than -57 KJ/mol, extra heat needed for acid to fully disassociate and then extra is subtracted from -57 KJ/mol at the end

30
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
where is this experiment carried out and why

A

in polystyrene cups at they are insulators

31
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
what must be known about substances before experiment starts

A

known volume and molarity

32
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
first reading that is taken (separately)

A

the temperature of each

33
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
3 essential things when carrying this out

A

do it very quickly
stir briefly
sensitive thermometer

34
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
why must you do it very quickly?

A

to ensure that heat was not lost to the surroundings

35
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
why do you stir?

A

to ensure uniform heat distribution throughout the solution so that an accurate temperature reading can be obtained

36
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
why is the stirring only brief?

A

as not to encourage more heat loss

37
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
formula

A

E = mcθ

38
Q

E

A

amount of energy produced by amount used

39
Q

m

A

mass of solution in KG

40
Q

c

A

specific heat capacity

41
Q

θ

A

rise in temperature

42
Q

density =

A

mass/volume

43
Q

DETERMINATION OF HEAT OF REACTION BETWEEN HYDROCHLORIC ACID AND SODIUM HYDROXIDE
if the 2 temperatures at the start are unequal

A

get an average

44
Q

bond broken

A

endothermic

requires energy

45
Q

bond made

A

exothermic

releases energy

46
Q

Bond energy

A

the energy requires to break 1 MOLE of covalent bonds and to separate the neutral atoms completely from each other

47
Q

energy profile diagrams =

A

reaction profile diagrams

48
Q

energy profile diagrams of endothermic reaction

A

products have more energy reactants

49
Q

energy profile diagrams of exothermic reaction

A

products have less energy than the reactants

50
Q

energy profile diagrams x axis

A

reaction coordinate

51
Q

energy profile diagrams y axis

A

energy

Chemistry (Tara) (50 decks)

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