Calculate the molar heat of reaction from the following data: CaO (s) + H 2 O (i

Question

Calculate the molar heat of reaction from the following data:

                                    CaO(s) + H2O(i) Ca(OH)2(aq)

50.23 mL H2O (at 23.5°C) were added to a styrofoam container before 0.514g CaO were added and allowed to react to completion. The maximum temperature reached by the solution was 27.5°C.

A) Determine the T

B) Mass of the system (density of water at 23.5 °C is 0.998g/mL)

C) Amount of heat liberated by (given off by) the system (the specific heat of water is 4.184 J/g*°C))

D) Calculate the heat liberated per mole of reactant (CaO = 56.08 g/mol)

E) What is the proper sign (negative or positive) for the heat of reaction of this system and why?

Explanation / Answer

ANSWER:

A) T = 27.5 - 23.5 = 4C

Heat is released in the process because the temperature of the system has increased.

Heat released in te process = mass X heat capacity X temperature change

Heat released = 50.2 X 4.184 X (27.5 - 23.5) = 840.14J

Hint: mass = volume X density

D) 0.514g of CaO results in release of 840.14 J of heat. One mole (56.08g) will result in 840.14 /0.514 X 56.08 = 91.66KJ of energy ( = Molar heat of the system)

E) The sign of heat of reaction is negative for the reaction as the energy is released. products will have less energy than reactants.

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