Chemistry Reference
In-Depth Information
b
Which way would the electrons flow in the wire
connected to the voltmeter - from 'copper to
zinc' or 'zinc to copper'?
c
Why should copper(ii)
ii
) sulfate crystallise at the
bottom of the outer container?
d
What is the function of the porous pot?
e
There are problems associated with the Daniell
cell which have led to it being replaced by other
types of cell. Give two reasons why Daniell cells
are no longer in use today.
5
This question is about endothermic and
exothermic reactions.
a
Explain the meaning of the terms endothermic
and exothermic.
b (i)
Draw an energy level diagram for the reaction:
NaOH(
aq
) + HCl(
aq
) → NaCl(
aq
) + H
2
O(
l
)
Δ
H
= −57 kJ mol
−1
(iii)
Is this reaction endothermic or exothermic?
(iii)
Calculate the energy change associated with
this reaction if 2 moles of sodium hydroxide
were neutralised by excess hydrochloric acid.
c (i)
Draw an energy level diagram for the reaction:
2H
2
O(
l
) → 2H
2
(
g
) + O
2
(
g
)
Δ
H
= +575 kJ mol
−1
(iii)
Is this reaction endothermic or exothermic?
(iii)
Calculate the energy change for this reaction
if only 9 g of water were converted into
hydrogen and oxygen.
6
The following results were obtained from an
experiment carried out to measure the enthalpy of
combustion (heat of combustion) of ethanol. The
experiment involved heating a known volume of
water with the flame from an ethanol burner.
The burner was weighed initially and after the
desired temperature rise had been obtained.
Volume of water in glass beaker = 200 cm
3
Mass of ethanol burner at start = 85.3 g
Mass of ethanol burner at end = 84.8 g
Temperature rise of water = 12 °C
(Density of water = 1 g cm
−3
)
Heat energy = mass of × 4.2 × temperature
water/g J g
−1
°C
−1
given to
rise/°C
water
a
Calculate the mass of ethanol burned.
b
Calculate the amount of heat produced, in joules,
in this experiment by the ethanol burning.
c
Convert your answer to
b
into kilojoules.
d
Calculate the amount of heat produced by 1 g of
ethanol burning.
e
What is the mass of 1 mole of ethanol
(C
2
H
5
OH)?
(
A
r
: H = 1; C = 12; O = 16)
f
How much heat would be produced if 1 mole
of ethanol had been burned? (This is the heat of
combustion of ethanol.)
g
Compare your value with the actual value of
1371 kJ mol
−1
and suggest two reasons for the
difference in values.
h
Write a balanced chemical equation to represent
the combustion of ethanol.
7
The following results were obtained from a
neutralisation reaction between 1 mol dm
−3
hydrochloric acid and 1 mol dm
−3
sodium
hydroxide. This experiment was carried out to
measure the heat of neutralisation of hydrochloric
acid. The temperature rise which occurred during
the reaction was recorded.
Volume of sodium hydroxide used = 50 cm
3
Volume of acid used = 50 cm
3
Temperature rise = 5 °C
(Density of water = 1 g cm
−3
)
Heat energy = mass of × 4.2 × temperature
given out
thermometer
water/g J g
−1
°C
−1
rise/°C
metal
calorimeter
during
reaction
a
Write a balanced chemical equation for the
reaction.
b
What mass of solution was warmed during the
reaction?
clamp
water
heat
draught
shield
