WorksheetsHess' Law
Total questions: 8
Worksheet time: 13mins
Name
Class
Date
1.
The enthalpy change for the reaction
C(s, graphite) + 1⁄2O2(g) --> CO(g) cannot be measured directly since some carbon dioxide is always formed in the reaction.
It can be calculated using Hess’s Law and the enthalpy changes of combustion of graphite and of carbon monoxide.
C(s, graphite) + O2(g) --> CO2 ΔH=-394 kJmol–1
CO(g) + 1⁄2O2(g) --> CO2 ΔH=-283 kJmol–1
The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is
C(s, graphite) + 1⁄2O2(g) --> CO(g) cannot be measured directly since some carbon dioxide is always formed in the reaction.
It can be calculated using Hess’s Law and the enthalpy changes of combustion of graphite and of carbon monoxide.
C(s, graphite) + O2(g) --> CO2 ΔH=-394 kJmol–1
CO(g) + 1⁄2O2(g) --> CO2 ΔH=-283 kJmol–1
The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is
a)
-677 kJmol–1
b)
+111 kJmol–1
c)
-111 kJmol–1
d)
+677 kJmol–1
2.
The enthalpy change for the reaction, ∆Hr , is equal to
a)
∆H1 + ∆H2
b)
∆H1 - ∆H2
c)
-∆H1 - ∆H2
d)
-∆H1 + ∆H2
3.
The enthalpies of combustion of C(s), H2(g) and C4H9OH(l) (in kJmol-1) are as follows
C(s) + O2(g) -> CO2(g) ∆H=a
H2(g) + ½O2(g) -> H2O(l) ∆H=b
C4H9OH(l) + 6O2(g) -> 4CO2(g) + 5H2O(l) ∆H=c
What is the enthalpy change for the reaction shown below?
4C(g) + 5H2(l) + ½O2(g) -> C4H9OH(l)
C(s) + O2(g) -> CO2(g) ∆H=a
H2(g) + ½O2(g) -> H2O(l) ∆H=b
C4H9OH(l) + 6O2(g) -> 4CO2(g) + 5H2O(l) ∆H=c
What is the enthalpy change for the reaction shown below?
4C(g) + 5H2(l) + ½O2(g) -> C4H9OH(l)
a)
c – 4a – 5b
b)
2a + 10b - c
c)
4a + 5b - c
d)
2a + 5b + c
4.
The standard enthalpy changes of combustion of carbon, hydrogen and methane are shown in the table.
Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol–1?
C(s) + 2H2(g) → CH4(g)
Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol–1?
C(s) + 2H2(g) → CH4(g)
a)
394 + (2 × 286) – 891
b)
–394 – (2 × 286) + 891
c)
394 + 286 – 891
d)
–394 – 286 + 891
5.
Given the following data: ΔH○f[FeO(s)] = –270kJmol–1
ΔH○f [Fe2O3(s)] = –820 kJ mol–1
Select the expression which gives the enthalpy change, in kJ mol–1, for the reaction:
2FeO(s) + 1⁄2O2(g) → Fe2O3(s)
ΔH○f [Fe2O3(s)] = –820 kJ mol–1
Select the expression which gives the enthalpy change, in kJ mol–1, for the reaction:
2FeO(s) + 1⁄2O2(g) → Fe2O3(s)
a)
(–820 × 1⁄2) + 270 = –140
b)
(+820 × 1⁄2) – 270 = +140
c)
–820 + (270 × 2) = –280
d)
+820 – (270 × 2) = +280
6.
The standard enthalpy changes of formation of iron(II) oxide, FeO(s), and aluminium oxide, Al2O3(s), are –266 kJ mol–1 and –1676 kJ mol–1 respectively.
What is the enthalpy change under standard conditions for the following reaction?
3FeO(s) + 2Al (s) -> 3Fe(s) + Al2O3(s)
What is the enthalpy change under standard conditions for the following reaction?
3FeO(s) + 2Al (s) -> 3Fe(s) + Al2O3(s)
a)
+878kJ
b)
–878kJ
c)
–1942kJ
d)
–2474kJ
7.
Use the chart to answer the following question.
Which is correct about energy changes during bond breaking and bond formation?
Which is correct about energy changes during bond breaking and bond formation?
a)
A
b)
B
c)
C
d)
D
8.
C2H4(g) + H2(g) -> C2H6(g) ∆H°=-137 kJ mol-1
Which statement about this information is correct?
Which statement about this information is correct?
a)
The total energy of the bonds broken in the reactants is greater
than the total energy of the bonds
formed in the product
than the total energy of the bonds
formed in the product
b)
The bonds broken and the bonds made are of the same strength
c)
The total energy of the bonds broken in the reactants is less than the total energy of the bonds formed in the product
d)
No conclusion can be made about the sums of the bond enthalpies in the product compared with the reactants
100 %
