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CHEM IGCSE > energetics > Flashcards

energetics Flashcards

1
Q

in an endothermic reaction,

A

energy is taken in from the surroundings

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2
Q

in an exothermic reaction,

A

energy is released into the surroundings

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3
Q

in an exothermic reaction, temperature of the surroundings

A

increases

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4
Q

what are 2 examples of exothermic reactions

A

combustion and neutralisation

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5
Q

in endothermic reactions, temperature of the surroundings

A

decreases

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6
Q

what is an example of an endothermic reaction

A

thermal decomposition

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7
Q

how do you remember if energy goes in or out in exo and endo reactions

A

EXO = EXits

ENDO- in

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8
Q

what is the law of conservation of energy

A

energy cannot be created or destroyed but it can be transferred

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9
Q

displacement reactions are endo or exo

A

can be both

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10
Q

neutralisation reactions are endo or exo

A

always exothermic

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11
Q

combustion reactions are endo or exo

A

always exothermic

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12
Q

what are the 2 types of calorimetry experiments

A

enthalpy changes of reactions in solution
enthalpy changes for combustion

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13
Q

to calculate the amount of energy produced by a chemical reaction in solutions what do we do

A
  • measure the temperature change when the solutions are mixed together
  • the solutions need to be mixed together in an insulated container to prevent heat loss
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14
Q

the method for reactions in solutions can be used for (3)

A
  • neutralisation reactions
  • dissolving solids
  • displacement reactions
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15
Q

what is the specific heat capacity of water

A

4.2

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16
Q

what is the density of water

A

1 g/cm³

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17
Q

in calorimetry experiments, what do we take for granted / assumptions (4)

A
  • the specific heat capacity of the solution is the same as pure water (4.2)
  • density of solution is same as pure water (1 g/cm³)
  • reaction is complete
  • specific heat capacity of the container is ignored
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18
Q

A calorimeter can be made up of and why

A

a polystyrene drinking cup, a vacuum flask or a metal can

because they’re insulating materials

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19
Q

how do you carry out a simple calorimetry experiment

A
  • have a polystyrene cup with a plastic lid to prevent heat loss
  • add one reagent
  • have a thermometer there and measure initial temperature
  • add the second reagent and stir continuosly
  • record the maximum temperature it reaches and record the rise
  • record energy released using Q=mcΔT
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20
Q

equation for energy released

A

Q = m x c x ΔT

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21
Q

what does Q stand for and units of measurement

A

heat energy change, J

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22
Q

what does m stand for and units of measurement

A

mass of the substance being heated, g

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23
Q

what does c stand for and units of measurement

A

specific heat capacity, J/g/°C

24
Q

what does ΔT stand for and units of measurement

A

temperature change, °C

25
Q

principle of a combustion calorimetry experiment

A

to use the heat released by a combustion reaction to increase the heat content of water

26
Q

method for enthalpy of combustion

A
  • fill copper calorimeter with 100cm³ of pure water
  • measure initial temp
  • weigh spirit burner
  • place spirit burner under calorimeter ( under specific distance)
  • light the spirit burner and leave for 2 mins
  • after 2 mins measure the final temp of the water
  • re-weigh the spirit burner
27
Q

In combustion calorimetry experiment the main sources of error are (2)

A

Heat losses

Incomplete combustion

28
Q

difference between the combustion experiment and the neutralisation etc.. experiment

A

combustion requires a spirit burner to burn

29
Q

what is enthalpy

A

energy

30
Q

what is molar enthalpy change

A

heat energy change per mole of substance

31
Q

how do you calculate molar enthalpy change

A

ΔH= Q / n

= heat energy change / number of moles

32
Q

molar enthalpy units

A

kJ/ mol

33
Q

enthalpy units

A

joules

34
Q

when calculating molar enthalpy change, what do you do to the enthalpy (Q) ( think of the units used)

A

need to divide by 1000, because molar enthalpy is measured in kilojoules while enthalpy is in joules

35
Q

moles can be figured out using 2 equations

A

mass / Mr

concentration x volume

36
Q

in molar enthalpy change, if the temperature of solution or water increased then the ΔH will be positive or negative and what reaction will it be

A

ΔH will be negative

exothermic reaction

37
Q

in molar enthalpy change, if the temperature of solution or water decreased then the ΔH will be positive or negative and what reaction will it be

A

ΔH will be positive

will be an endothermic reaction

38
Q

for an energy level diagram for exothermic reactions, how will the reactant and product lines look

A

as energy is being released, the reactant will be higher than the products

39
Q

draw an exothermic energy level diagram

A

reactant will be higher than the products, add the arrow pointing down in the middle of then saying that energy is released

40
Q

for an energy level diagram for endothermic reactions, how will the reactant and product lines look

A

products will have more energy than the reactants so the line will be higher up

41
Q

draw an endothermic energy level diagram

A

reactant line will be low

arrow be pointing up saying energy is absorbed

product line will be high

42
Q

what are the two labels ( x and y) for an energy level diagram

A

energy - y

progress of reaction - x

43
Q

when drawing energy level diagrams, should you state the name of the products and reactants on the line

A

YES

44
Q

bond breaking is an _______ reaction because

A

endothermic reaction,
energy must be supplied to existing bonds in order to break them

45
Q

bond forming is a _______ reaction because

A

exothermic
energy is released

46
Q

total change for enthalpy for a reaction can be calculated if we know

A

the bond energies of all the species involved

47
Q

enthalpy change calculation

A

energy taken in - energy given out

48
Q

each bond has a ___ energy

A

bond

49
Q

what are bond energies

A

amount of energy needed to break the bond or the amount of energy given out when the bond is formed

50
Q

for exothermic reactions, enthalpy change will be positive or negative

why

A

negative

product will have more energy than reactant

51
Q

for endothermic reactions, enthalpy change will be positive or negative

why

A

positive

product will have less energy than reactant

52
Q
A
53
Q

an exothermic reaction will occur if ( bond energies)

A

more energy is released when new bonds are formed than what was needed to break them

54
Q

an endothermic reaction will occur if ( bond energies)

A

if the energy taken in to break the bonds exceeds the energy when new bonds are formed

55
Q

INVESTIGATE temperature changes

A

Using a measuring cylinder, place 25 cm3 of the NaOH solution into the calorimeter

Measure and record the temperature of the solution

Add 5 cm3 of the dilute HCl and stir

Measure and record the highest temperature reached by the mixture

Repeat steps 1 – 4 increasing the amount of acid added by 5 cm3 each time

CHEM IGCSE (31 decks)

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