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More
revision questions
Francine
Taylor-Campbell, Contributor
We
will examine some more questions as
part of your examination preparations.
Question
1
1.
The following results were obtained
by burning methane and using the energy
obtained to heat a known mass of water:
Mass
of water = 250g
Initial
temperature of water = 26°C
Final temperature of water = 36°C
Mass of methane = 0.2g
Use
this information to calculate the
heat of combustion in KJ per mole
of methane. Assume that there are
no heat losses and that the 4.2J of
energy are needed to raise the temperature
of 1g of water by 1°C.
ANSWERS
Q1.
Heat change for rxn = mass of soln
x heat capacity of soln x temperature
change. This is an equation worth
remembering!
DH
= 250g x 4.2 Jg-1C-1 x 10 C = 10.5
KJ
This
energy change was given out from the
burning of 0.2g of methane.
1
mole of methane (CH4) has a mass of
(12 + 4) = 16g
#
mol in 0.2g = 0.2/16 = 0.0125 mol
Thus
0.0125 mol give out 10.5 KJ of heat
1
mole = 10.5/0.0125 = 840 KJ/mol
Now
attempt this question.
Question
2
2.
Give the equation for the reaction
between methane and steam.
Calculate
the maximum volume of hydrogen, measured
at s.t.p., which can be obtained from
16g of methane.
Answers
(a)
CH4 (g) + H2O
(g) ? CO (g) + 3H2 (g)
(b)
Mr of CH4 =
12+ (1*4) = 16
#mol
CH4 = 16/16 = 1 mol
Based
on reaction, 1 mol of CH4
produces 3 mol of H2 gas
At
s.t.p, 1 mol of any gas = 22.4 dm-3
Volume
of 3 mol H2 = 3*22.4 =
67.2 dm-3
To
ensure that you are properly preparing
for your exams, try practising past-paper
questions under exam conditions. That
is, try answering the questions in
the time normally set for the exams.
In this way you get used to working
fast and with a time limit.
Good
luck in your exams and continue to
study hard!
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Carolyn
Supersad (left), promotions
manager for PediaSure at Cari-Med,
greets students at the Covenant
Christian Academy and Children's
Centre (from second left) Khori
Bennett, Ashli Findlator and
Robyn-Leigh Hearne. PediaSure
is the official drink of the
Covenant/Globe Over-Distance
Track Meet, now in its 10th
year. They were at the launch
of the meet on April 14 at Globe
Insurance Company in New Kingston.
- Contributed
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Francine
Taylor-Campbell is an independent
contributor.
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