CHEM 210 MODULE 3 EXAM QUESTIONS AND CORRECT ANSWERS, WITH COMPLETE SOLUTION 2024.
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CHEM 210 MODULE 3 EXAM QUESTIONS AND CORRECT ANSWERS, WITH COMPLETE SOLUTION 2024.
What is meant by the term average bond enthalpy?
(Average enthalpy change) when one mole of bonds
of (gaseous covalent) bonds is broken
The calculated value of ΔHc from this experiment is different from the ...
chem 210 module 3 exam questions and correct answe
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CHEM 210 MODULE 3 EXAM QUESTIONS AND CORRECT
ANSWERS, WITH COMPLETE SOLUTION 2024.
What is meant by the term average bond enthalpy?
(Average enthalpy change) when one mole of bonds
of (gaseous covalent) bonds is broken
The calculated value of ΔHc from this experiment is different from the value
obtained
from data books.
Apart from heat loss, suggest two reasons for the difference.
Assume that the calculation has been carried out correctly.
incomplete combustion
non-standard conditions
evaporation of alcohol/water
specific heat capacity of beaker/apparatus
The enthalpy change of combustion for alcohol J can also be determined
indirectly from
standard enthalpy changes of formation.
(i) Write an equation, including state symbols, for the chemical change that
represents the
standard enthalpy change of formation of the liquid alcohol J, C5H12O.
5C(s) + 6H2(g) + 1⁄2O2(g) ⎯→ C 5H12O(l)
A closed system is required for dynamic equilibrium to be established.
State one other feature of this dynamic equilibrium.
Rate of the forward reaction is equal to the rate of the reverse
reaction
OR
concentrations do not change
The student heats the equilibrium mixture keeping the volume constant.
Predict how the composition of the equilibrium mixture changes on heating.
Explain your answer.
More H2 and I2 OR less HI
(equilibrium position shifts) to the left
AND
(Forward) reaction is exothermic
OR reverse reaction is endothermic
OR in the endothermic direction
A student mixes hydrogen and iodine at room temperature and pressure and
allows the
mixture to reach dynamic equilibrium.
H2(g) + I2(g) 2HI(g) ΔH = −9 kJ mol−1 equilibrium 3.1
Predict and explain what effect, if any, an increase in the pressure would have on the
position of the equilibrium.
No effect
AND
Same number of (gaseous) moles on both sides
............................................................
What is meant by the term standard enthalpy change of formation?
Give the standard conditions.
(Enthalpy change) when one mole of a compound
is formed from its elements
298 K / 25 °C AND 1 atm / 100 kPa / 101 kPa / 1 bar
Describe and explain, using equations, how the concentration of ozone in the
stratosphere is
maintained.
O3 O2 + O AND O + O2 O3
rate of ozone decomposition (almost) equals rate of ozone
formation
In the stratosphere, NO catalyses the breakdown of ozone.
Write two equations to show how NO catalyses this breakdown.
NO + O.3 NO2 + O2
NO2 + O NO + O2
It is not possible to measure the enthalpy change of formation of N2O(g) directly.
Suggest why it is not possible.
It is very difficult to determine the standard enthalpy change of formation of
hexane
directly. Suggest a reason why.
Reaction gives NO OR reaction gives NO2 OR reaction
gives a mixture of oxides OR activation energy too high
OR rate of reaction is too slow
Methane is a greenhouse gas. Scientists are concerned that the concentration of
methane in
the atmosphere is slowly increasing.
(i) Explain how atmospheric methane molecules can contribute to global
warming.
Absorbs IR radiation
Bonds vibrate
One way that scientists hope to minimise global warming is by developing
Carbon
Capture and Storage, CCS, techniques.
Describe two of these CCS techniques.
(liquid) injected deep into the oceans
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