# Enthalpy 2 (Worksheets)


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Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

## Q1

Calculate the $$\Delta{H^o_{rxn}}$$ from the $$\Delta{H^o_f}$$ for the following reaction:

1. $PbO_{(s)} + CO(g) \rightarrow Pb(s) + CO_2 (g) \nonumber$
2. $SiH_{4 \,(g)} + 2 O_2 (g) \rightarrow SiO_2 (s) + 2 H_2O (l) \nonumber$
3. $2 FeS_{2\, (s)} + 5.5 O_2 (g) \rightarrow Fe_2O_3 (s) + 4 SO_2 (g) \nonumber$
$$\Delta{H^o_f}$$ kJ/mol
$$\Delta{H^o_f}$$ kJ/mol
$$CO_{(g)}$$
-110.5
$$Pb_{(s)}$$
0
$$CO_{2\,(g)}$$
-393.5
$$PbO_{(s)}$$
-217.3
$$Fe_2O_{3\,(s)}$$
-824.2
$$SiH_{4\,(g)}$$
34.3
$$FeS_{2\,(s)}$$
-177.5
$$SiO_{2\,(s)}$$
-910.9
$$H_2O_{(l)}$$
-285.8
$$SO_{2\,(g)}$$
-296.8
$$O_{2\,(g)}$$
0

## Q2

Determine the $$\Delta{H^o_{rxn}}$$ using Hess's Law

a) Determine the enthalpy of formation for $$MnO_{2\,(s)}$$

$Mn_{(s)} + O_{2\,(g)} \rightarrow MnO_{2\,(s)} \nonumber$

Given:

$4Al_{(s)} + 3O_{2\,(g)} \rightarrow 2Al_2O_{3\,(s)} \nonumber$

with $$\Delta H$$ = -3352 kJ/mol

$4Al_{(s)} + 3MnO_{2\,(s)} \rightarrow 3Mn_{(s)} + 2Al_2O_{3\,(s)} \nonumber$

with $$\Delta H$$ = -1937 kJ/mol

b) Determine the heat of hydrogenation for

$C_3H_{4\,(g)} + 2H_{2\,(g)} \rightarrow C_3H_{8\,(g)} \nonumber$

Given:

$2H_{2\,(g)} + O_{2\,(g)} \rightarrow 2H_2O_{2\,(l)} \nonumber$

with $$\Delta H$$ = -571.6 kJ/mol

$C_3H_{4\,(g)} + 4O_{2\,(g)} \rightarrow 3CO_{2\,(g)} + 2H_2O_{(l)} \nonumber$

with $$\Delta H$$ = -1937 kJ/mol

$C_3H_{8\,(g)} + 5O_{2\,(g)} \rightarrow 3CO_{2\,(g)} + 4H_2O{(l)} \nonumber$

with $$\Delta H$$ = -2220 kJ/mol

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