|AP Chemistry -- Thermochemistry
||What is meant by the term chemical
||What is meant by an energy source?
||How many kilocalories are in
||Which of these are exothermic
|a) N2 + 3 H2
----> 2 NH3
delta Horxn = -92.05 kJ
|b) 2 HgO + 181.17 kJ ----> 2
Hg + O2
+ 3 CO ----> 2 Fe + 3 CO2 + 27.61 kJ
|d) N2 + O2
----> 2 NO - 180.75 kJ
||How many kilojoules of heat energy
are absorbed in raising the temperature of 10.0 grams of water from 5oC
||The specific heats of gold, silver
and copper are 0.13, 0.24, and 0.39 J g-1 K-1,
If one gram samples of each, at room temperature, are placed in the
beaker of hot water,
|a) the temperature of all three
samples will be different at the end.
|b) the gold will gain the greatest
quantity of heat.
|c) the copper will
gain the greatest quantity of heat.
|d) at the end the gold will be
at the highest temperature.
|e) initially, the temperature
of the copper will rise the fastest.
||Fat tissue is 85% fat and 15%
water. The complete breakdown of the fat itself converts it to CO2
and H2O, and releases about 37.665 kJ/g (of fat in the fat
|(a) How many kilojoules are released
by a loss of 0.45 kg (1 lb.) of fat tissue in a weight-reduction
|(b) A person running at 13 km/hr
expends about 2.0 X 103 kJ/hr of extra energy. How far does
a person have to run to "burn off" 0.45 kg of fat tissue by this means
||A well-nourished person adds
about 0.23 kg of fat tissue for each 83.65 kJ of food energy taken in
and above that needed. Suppose that you decide to reduce your weight
by omitting butter but keeping every other aspect of your diet and your
activities the same. How many days would be needed to lose 4.3 kg of
tissue by this strategy alone? The energy content of butter is 37.65
Suppose that you have been eating 1.1 g of butter a day.
||What is the molar heat capacity
of ethyl alcohol, C2H5OH, in units of J/moloC,
if its specific heat is 0.586 cal/goC?
||The specific heat of helium is
5.188 J/goC and of nitrogen is 1.042 J/goC. How
joules can one mole of each gas absorb when its temperature increases
||We wish to determine how much
heat paraffin gives off on burning. We use a candle flame to heat some
water in a calorimeter. These data were obtained:
Mass of water in
Initial mass of
candle 150 g
Final mass of candle
Final temperature of
a) the temperature
b) the joules
absorbed by the
water in the calorimeter,
c) the grams of
d) the approximate
value of heat
of combustion of paraffin in J/g.
Neglect the energy
||During the combustion of wax,
2.00 grams of wax were consumed. The heat was collected in 100.0 grams
of a liquid (not water) and the temperature of the liquid increased by
20.0oC. If the heat of combustion of the wax is 450 kJ/kg,
the specific heat capacity of the unknown liquid.
||Trimgristin, extracted from nutmegs,
has a melting point of 56oC and a boiling point of 311OC.
Sketch the heating curve of this substance from 50oC to 350oC.
Identify the processes that occur at each portion of the curve.
||14. Aluminum and iron(III) oxide,
Fe2O3, react and form aluminum oxide, Al2O3,
and iron. For each mole of aluminum used, 426.9 kJ of energy is
under standard conditions. Write the thermochemical equation that shows
the consumption of 4 mol of Al. (All substances are solids)
||The following equation represents
the dehydration of calcium hydroxide to make quicklime, CaO, a
present in cement.
CaO(s) + H2O(l) delta Horxn = +65.3 kJ
One of the
reactions when cement
is mixed with water is the reverse of this reaction. Write the
equation for the reaction of 10 mol of quicklime with water under
||A sample of 10.1 g of ammonium
nitrate, NH4NO3, was dissolved in 125 g of water
in a coffee cup calorimeter. The temperature changed from 24.5oC
to 18.8oC Calculate the heat of solution of ammonium nitrate
in kJ/mol. Assume that the energy exchange involves only the solution
that the specific heat of the solution is 4.18 J/goC.
||Barium oxide, BaO, can be used
to neutralize pure sulphuric acid, H2SO4. The
BaO(s) + H2SO4(l) ----> BaSO4(s) + H2O(l)
What is the
change of this reaction? The following thermochemical equations can be
SO3(g) + H2O(l)
> H2SO4(l) delta Horxn=
BaO(s) + SO3(g)
BaSO4(s) delta Horxn = -213 kJ
||What is the value for delta Horxn
of neutralization of lithium hydroxide, LiOH(aq), by hydrochloric acid,
HCl(aq), by the following equation?: LiOH(aq) +
-------> LiCl(aq) + H2O(l)
can be used in addition to any prepared equations, as needed from a
Li(s) + ½ O2(g)
+ ½ H2(g) ----> LiOH(s) delta Horxn=
2 Li(s) + Cl2(g)
2 LiCl(s) delta Horxn= -815.0 kJ
Horxn= -19.2 kJ
HCl(aq) delta Horxn=
Horxn= -36.0 kJ
||Given these two reaction heat
S(s) + O2(g)
SO2(g) delta Horxn=-295 kJ/mol and
S(s) + 3/2 O2(g)
-----> SO3(g) delta Horxn=-395
what is the heat
of reaction for
----> 2 SO3(g) under the same
||Which one of the following processes
is expected to involve the smallest energy change?
a. Condensing, at 25oC,
one mole of water vapour
b. Nuclear fission of
c. Reacting two moles
atoms to make one mole of H2(g).
d. Fusion of one mole
nuclei with one mole of helium nuclei to make lithium nuclei.
e. Mixing one mole of
two reactants which liberate 200 kJ.
||For the reaction, H2(g)
+ I2(g) -------> 2HI(g), Ho=+52.0
Which statement is INCORRECT?
a. The heat of
formation of one
mole of HI(g) is +26.0 kJ.
b. H2 and I2
are energy poor compared to HI.
c. The temperature
as the reaction proceeds.
d. Heating will cause
to proceed to the left.
||Arrange the steps below in the
proper order to determine the molar heat of solution of a salt.
1. Add salt to water
well to dissolve the salt.
2. Calculate the heat
3. Determine the
change in temperature.
4. Measure the
5. Record the
6. Weigh the salt to
and calculate number of moles of salt.
The correct order
a. 6, 4, 5, 3, 1, 2
b. 6, 4, 5, 1, 3, 2
c. 6, 4, 1, 5, 3, 2
d. 6, 1, 4, 5, 3, 2
||Which of the following are endothermic?
--------> 3C(s) + 4 H2(g) H = +84 kJ
(2) ½ N2(g)
+ 1½H2(g) --------> NH3(g)
H2O(g) H = ?
+ heat N2(g)
+ ½ O2(g)
a. 1 and 2
b. 1 and 3
c. 2 and 4
e. 1, 3, 4
||When 4.32 grams of HgO(s) forms
from its elements how much heat is involved in kJ?
e. none of these