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
