CHEM IGCSE > energetics > Flashcards

energetics Flashcards

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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

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24
Q

what does ΔT stand for and units of measurement

A

temperature change, °C

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25
principle of a combustion calorimetry experiment
to use the heat released by a combustion reaction to increase the heat content of water
26
method for enthalpy of combustion
- 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
In combustion calorimetry experiment the main sources of error are (2)
Heat losses Incomplete combustion
28
difference between the combustion experiment and the neutralisation etc.. experiment
combustion requires a spirit burner to burn
29
what is enthalpy
energy
30
what is molar enthalpy change
heat energy change per mole of substance
31
how do you calculate molar enthalpy change
ΔH= Q / n = heat energy change / number of moles
32
molar enthalpy units
kJ/ mol
33
enthalpy units
joules
34
when calculating molar enthalpy change, what do you do to the enthalpy (Q) ( think of the units used)
need to divide by 1000, because molar enthalpy is measured in kilojoules while enthalpy is in joules
35
moles can be figured out using 2 equations
mass / Mr concentration x volume
36
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
ΔH will be negative exothermic reaction
37
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
ΔH will be positive will be an endothermic reaction
38
for an energy level diagram for exothermic reactions, how will the reactant and product lines look
as energy is being released, the reactant will be higher than the products
39
draw an exothermic energy level diagram
reactant will be higher than the products, add the arrow pointing down in the middle of then saying that energy is released
40
for an energy level diagram for endothermic reactions, how will the reactant and product lines look
products will have more energy than the reactants so the line will be higher up
41
draw an endothermic energy level diagram
reactant line will be low arrow be pointing up saying energy is absorbed product line will be high
42
what are the two labels ( x and y) for an energy level diagram
energy - y progress of reaction - x
43
when drawing energy level diagrams, should you state the name of the products and reactants on the line
YES
44
bond breaking is an _______ reaction because
endothermic reaction, energy must be supplied to existing bonds in order to break them
45
bond forming is a _______ reaction because
exothermic energy is released
46
total change for enthalpy for a reaction can be calculated if we know
the bond energies of all the species involved
47
enthalpy change calculation
energy taken in - energy given out
48
each bond has a ___ energy
bond
49
what are bond energies
amount of energy needed to break the bond or the amount of energy given out when the bond is formed
50
for exothermic reactions, enthalpy change will be positive or negative why
negative product will have more energy than reactant
51
for endothermic reactions, enthalpy change will be positive or negative why
positive product will have less energy than reactant
52
53
an exothermic reaction will occur if ( bond energies)
more energy is released when new bonds are formed than what was needed to break them
54
an endothermic reaction will occur if ( bond energies)
if the energy taken in to break the bonds exceeds the energy when new bonds are formed
55
for salts dissolving (ammonium nitrate) would it be a endo or exo thermic reaction and why
endothermic because temperature decreases
56
for salts dissolving (calcium chloride) would it be a endo or exo thermic reaction and why
exothermic because temperature increases
57
for neutralisation reactions, is it endo or exothermic and why
exothermic because temperature increases
58
for displacement reaction, is it endo or exo and why
exo because temp increases
59
for combustion, is it endo or exo and why
exo because temp increases
60
How would you measure temperature change in displacement?
Measure temp of metal salt solution, add metal, record temp change
60
How would you measure temperature change in neutralisation?
Mix acid and alkali, record temp before and after mixing
61
How would you measure temperature change when salt dissolves?
Measure temp of water, add salt, stir, record temp after dissolving
62
How would you measure temperature change in combustion?
Burn fuel under water in a can, measure water temp before and after
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