A total of 2.00 mol of a compound is allowed to react with water in a foam coffe

Question

A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 145 g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 . What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.

This is what I do:

q = (c)(m)(T)

q = (4.18 J/g*K) (145 g) (24.70-21)

q = 2242.57 J Change to negative because reaction is exothermic:

q = -2242.57 Change to kJ

q = -2.24257 Divide by the inital 2 mols to get kJ per mole as answer:

q = -2.24257 / 2 mol

Final answer = -1.21285 kJ

Mastering Chemistry wants three sig figs = -1.21 kJ/mol

MASTERING CHEMISTRY SAYS THAT IS WRONG. What did I do incorrect?

Explanation / Answer

You procedure is absolutely correct .

But in last step. q = -2.24257 / 2 mol

= 1.121285 kj/mol.

But you are entering 1.21

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