CHEM 110
State function
1. Referring to the picture above, which of these
statements are true?
i.
ii.
iii.
The distance travelled from A to B along
the straight line path is a state function.
The distance travelled on the curved path
from A to B is a state function.
The change in elevation from point A to B
(Δ) is a state function.
-------------------------------------------------------------------------------------------------------------------Which of the following is NOT a state function?
i.
internal energy (E)
ii.
heat (q)
iii.
enthalpy (H)
--------------------------------------------------------------------------------------------------------------------2. The contents of the boxes represents the system and everything outside the box is
the surroundings. The lengths of the arrows are proportional to the magnitude of the
energy changes associated with these processes.
i)
ii)
iii)
w in (work done on system) is greater than q out
w is done on system so internal energy increases.
q in is great than w out (work done by the system)
2A. Which of these processes is exothermic?
2B. Which of these processes is endothermic?
2C. Which of these processes has a net increase in internal energy?
--------------------------------------------------------------------------------------------------------------------3A. Circle the substance in each pair that has higher enthalpy at the same temperature.
Figu re 0 5.26 -02U NEOC
1. One mole of H2O(s)
2. One mole of H2O()
3. One mol of H2(g)
+ 0.5 mol O2(g)
one mole of H2O()
two mole of H2O()
one mole of H2O()
3B. The complete combustion of a hydrocarbon is exothermic. Draw an energy diagram
for this reaction.
--------------------------------------------------------------------------------------------------------------------4A. Given the following thermochemical equation. Determine the change in enthalpy
when 28.0 g of carbon monoxide is oxidized to carbon dioxide?
2CO (g) + O2 (g) → 2CO2 (g)
∆H = +566 kJ
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Recitation 14
CHEM 110
--------------------------------------------------------------------------------------------------------------------4B. How much heat is released when 25.0 g Na2O2 undergo this reaction?
2 Na2O2 (s) + 2 H2O () → 4 NaOH (s) + O2 (g)
ΔHº = −126 kJ
--------------------------------------------------------------------------------------------------------------------5A. When solid sodium hydroxide dissolves in water, the ΔH for the solution process is
−44.4 kJ/mol. If a 13.9-g sample of NaOH dissolves in 250.0 g of water in a coffeecup calorimeter initially at 23.0 °C. What is the final temperature of the solution?
Assume that the solution has the same specific heat as liquid water, i.e., 4.18 J/g-K.
--------------------------------------------------------------------------------------------------------------------5B. The temperature of 500.0 g water contained in a calorimeter increased from 20.0
o
C to 50.0 oC when 5.00 g of fuel was burned to completion. What is the ΔH of this
combustion reaction? (The specific heat of water is 4.184 J/g oC and the molecular
weight of the fuel is 40.0 g/mol)
--------------------------------------------------------------------------------------------------------------------6. Given the data in the table below, what is ΔH for this reaction?
Ca(OH)2(s) + 2 H3AsO4(aq) → Ca(H2AsO4)2(aq) + 2 H2O()
Substance
ΔHf° (kJ/mol)
Ca(OH)2(s)
–986.6
H3AsO4(aq)
–900.4
Ca(H2AsO4)2(aq)
–2346.0
–285.9
H2O()
--------------------------------------------------------------------------------------------------------------------7. What is the heat of reaction (ΔHrxno) for the combustion of acetone (C3H6O) given the
following thermochemical equations?
3 C (s) + 3 H2 (g) + ½ O2 (g) à C3H6O ()
C (s) + O2 (g) à CO2 (g)
H2 (g) + ½ O2 (g) à H2O ()
ΔHfo = −285.0 kJ/mol
ΔHfo = −394.0 kJ/mol
ΔHfo = −286.0 kJ/mol
--------------------------------------------------------------------------------------------------------------------8. Δ H for the reaction below is −57 kJ. Use the table of bond dissociation energies to
find the bond energy for H−Br.
H
H
C C
H
Bond:
D (kJ/mol)
+
H H
H C C Br
H H
HBr
H
C—C
348
C=C
614
C⎯H
413
C⎯Br
276
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Recitation 14