A 2.00 g sample of a salt (MX_(s)) is added to 20.0 g of water at 22.0 degree C

Question

A 2.00 g sample of a salt (MX_(s)) is added to 20.0 g of water at 22.0 degree C in a calorimeter. The maximum calculated temperature is 23.3 degree C. If the specific heat of the salt is 0.663 J/degree C-g, what is the enthalpy of solution for the salt MX if its molar mass is 68.0 g/mol? Based on your answer for #3 (above), what is delta H_f (X_(aq))? Use formation equations to find your answer. Failure to do so will result in zero credit. Delta H_f (MX_(s)) = -385.4 kJ/mol; delta H_f (M*_(aq) = -298.4 kJ/mol

Explanation / Answer

Question 4.

Te value of the enthalpy of solution must be NEGATIVE. since it is EXOTHERMIC, meaning it increases the surroundings temperature

The formation equation:

MX(s) --> M+(aq) + X-(aq)

HRxn = H-M+(aq) + H-X-(aq) - MX(s)

HRxn previous examples = Q/n = 110.6/(2/68) = 3760.4 J = -3.76 kJ

so

-3.76 = -298.4 + H-X- - (-385.4)

H-x = -3.76+298.4-385.4

H-X = -90.76 kJ/mol

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