# Hess's Law (Worksheet)

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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.

A 505 g piece of copper tubing is heated to 99.9°C and placed in an insulated vessel containing 59.8 g of water at 24.8°C. Assuming no loss of water and a heat capacity for the vessel of 10.0 J/K, what is the final temperature of the system?

## Q2.

Calculate the $$\Delta{H_{rxn}}$$ for

$Ca_{(s)} + \frac{1}{2}O_2 + CO_2 \rightarrow CaCO_3$

Given:

$Ca + \frac{1}{2}O_2 \rightarrow CaO \;\;\;\;\; \Delta{H} = -635.1 \;kJ$

$CaCO_3 \rightarrow CaO + CO_2 \;\;\;\;\; \Delta{H} = 178.3\; kJ$

## Q3.

Calculate $$\Delta{H_{rxn}}$$ for:

$2NOCl \rightarrow N_2 + O_2 + Cl_2$

Given:

$\frac{1}{2}N_2 + \frac{1}{2}O_2 \rightarrow NO \;\;\;\;\; \Delta{H} = 90.3\; kJ$

$NO + \frac{1}{2}Cl_2 \rightarrow NOCl \;\;\;\;\; \Delta{H} = -38.6\; kJ$

## Q4.

Calculate the $$\Delta{H_{rxn}}$$ for the following reactions:

$$2H_2S_{(g)} + 3O_{2\;(g)} \rightarrow 2SO_{2\; (g)} + 2H_2O (g)$$

$$CH_{4\;(g)} + 4Cl_{2\;(g)} \rightarrow CCl_{4\;(l)} + 4HCl_{(g)}$$

$$SiO_{2\; (s)} + 4HF_{(g)} \rightarrow SiF_{4 (g)} + 2H_2O_{(l)}$$