Question

A generic solid, X, has a molar mass of 78.2 g/mol. In a constant-pressure calorimeter, 12.6 g of X is dissolved in 337 g of water at 23.00 °C.X(s) yeilds X(aq)The temperature of the resulting solution rises to 24.40 °C. Assume the solution has the same specific heat as water, 4.184 J/(g·°C), and that there\'s negligible heat loss to the surroundings. How much heat was absorbed by the solution?What is the enthalpy of the reaction?

Answer 1

Answer:

a) Q = 2047.8 J (ΔH is negative because it's an exothermic reaction)

b) ΔH = -12.7 kJ /mol

Explanation:

Step 1: Data given

Molar mass of X = 78.2 g/mol

In a constant-pressure calorimeter, 12.6 g of X is dissolved in 337 g of water at 23.00 °C.

The temperature rise to 24.40 °C

The specific heat of the solution = 4.184 J/g°C

Step 2: Calculate the total mass

Total mass of the solution is given by  

Total mass = 12.6 grams + 337 grams = 349.6 grams

Step 3: Calculate heat

Q = m*c*ΔT

⇒ m = the total mass = 349.6 grams

⇒ c = the specific heat of solution = 4.184 J/g°C

⇒ ΔT = The change of temperature = T2 - T1 = 24.40 - 23.00 = 1.40 °C

Q = 2047.8 J (ΔH is negative because it's an exothermic reaction)

What is the enthalpy of the reaction?

Calculate number of moles = mass/ molar mass

Moles X = 12.6 grams / 78.2 g/mol

Moles X = 0.161 moles

ΔH = -2047.8 J / 0.161 moles

ΔH = -12719.3 J/mol = -12.7 kJ /mol