Question

you wish to prepare a hot pack that will generate a temp. of 78C (172.5 F) if your hot pack initally contains 150ml of water at 22C what mass of CaCl2 will you need to include in your hot pack?
Assume the specific hea of the resulting solution is 1.0 cal/g(C)

Answer 1

Answer on Question #56149 – Chemistry - General Chemistry

Question:

You wish to prepare a hot pack that will generate a temperature of 78°C (172.5 F) if your hot pack initially contains 150 ml of water at 22°C what mass of CaCl₂ will you need to include in your hot pack?

Assume the specific heat of the resulting solution is 1.0 cal/g(C).

Answer:

Heat of the reaction can be calculated as:

$$q = SH \cdot m \cdot \Delta T$$

where SH – specific heat of the reaction solution, cal/g(C);

ΔT - change in temperature (in °C);

m – mass of the solution, g.

$$q = 1.0 \cdot (150 + x) \cdot (78 - 22)$$ $$\mathrm{CaCl}_{2(\mathrm{s})} + \mathrm{H}_{2}\mathrm{O}_{(\mathrm{l})} = \mathrm{CaCl}_{2(\mathrm{aq})}$$ $$\Delta H_{\text{soln}} = -19.5 \ \mathrm{kcal/mol}$$ $$- q_{\text{reaction}} = q_{\text{calorimeter}}$$ $$19500 = 1.0 \cdot (150 + x) \cdot (78 - 22)$$ $$x = 19500 / 56 - 150$$ $$x = 198 \ \mathrm{g}$$

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