16 End-of-chapter test

16 End-of-chapter test
Enthalpy changes
This question refers to the following chemical changes:
i the thermal decomposition of calcium carbonate
ii the complete combustion of methane
iii respiration of glucose
iv photosynthesis.
a Write a balanced chemical equation for each change.
b Which changes are exothermic and which are endothermic?
c Draw labelled enthalpy profiles for respiration and photosynthesis.
d On one of these enthalpy profiles label clearly the part of the profile in which bonds are
being broken and the part in which bonds are being made.
a standard conditions
b standard enthalpy change of formation
c standard enthalpy change of combustion
d average bond enthalpy.
In an experiment, a spirit burner is used to heat 250 cm3 of water by burning methanol (CH3OH).
Ar: C = 12.0, H = 1.0, O = 16.0. Specific heat of water = 4.18 J g–1 °C–1
starting temperature of water = 20.0 °C
starting mass of burner + fuel = 248.8 g
final temperature of water = 43.0 °C
final mass of burner + fuel = 245.9 g
a How many joules of heat energy went into the water?
b How many moles of fuel were burnt?
c Calculate an experimental value for the enthalpy of combustion of methanol from
these results.
d Suggest three reasons why your answer is much smaller than the accepted standard
enthalpy of combustion of methanol.
Use the average bond enthalpies that follow to calculate a value for the enthalpy change of
this reaction:
H2 + I2 → 2HI
H–H = +436 kJ mol–1
I–I = +151 kJ mol–1
H–I = +299 kJ mol–1
Use the standard enthalpies of combustion that follow to calculate a value for the enthalpy
change of this reaction:
C6H5OH + 3H2 → C6H11OH
C6H5OH = –3064 kJ mol–1
H2 = –286 kJ mol–1
C6H11OH = –3727 kJ mol–1
COAS Chemistry 1 Teacher Resources
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