Instant hot packs work by crystallizing sodium acetate (NaCH3COO). The molar enthalpy of crystallization for sodium acetate is -56.7 kJ/mol. How many grams of sodium acetate are needed to warm 125.0 mL of water from 21.0 oC to 35.4oC?
The molar enthalpy of crystallization for sodium acetate is -56.7 kJ/mol
And latent heat of vaporisation of water is 40.662 KJ/mol
Amount of heat required to raise the temperature of 125 ml of H2O from 21°C to 35.4°C
Density of water is = 1 g/ml
That means we have 125 g of H2O
OR
125/18=6.94 mole of water
Total amount heat to raise temperature is =nC∆t
=6.94×40.662×14.4
=4066.2 KJ/mol
No of mole of sodium acetate required is
=4066.2 / 56.7
=71.71 mole of sodium acetate
Mass of sodium acetate required
=No. Of mole sodium acetate×molecular Mass of sodium acetate
=71.71×82
=5880.6 g of sodium acetate
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