Question

When 15.00 grams of potassium cyanide is dissolved in 52.0 grams of water initially at a temperature of 30.00 °C, the temperature of the solution decreases to 20.37 °C. Calculate deltaH for the reaction below in kJ/mol.

Answer 1

To calculate ΔH for the reaction, we can use the equation q = mcΔT. First, calculate the heat gained or lost by the water using its specific heat capacity and the given mass and temperature change. Then, use the calculated heat and the amount of solute to calculate ΔH.

Step-by-step explanation:

In order to calculate ΔH for the given reaction, we need to use the equation: q = mcΔT. Here, q represents the heat gained or lost, m represents the mass of the solution, c represents the specific heat capacity of the solution, and ΔT represents the change in temperature. First, we need to calculate the heat gained or lost by the water using its specific heat capacity and the given mass and temperature change. Then, we can use the calculated heat and the amount of solute to calculate ΔH.

Given:
Mass of potassium cyanide (KCN) = 15.00 g
Mass of water = 52.0 g
Initial temperature of water = 30.00 °C
Final temperature of solution = 20.37 °C
Specific heat capacity of water = 4.184 J/g°C (or 1 cal/g°C)

1. Calculate the heat gained or lost by the water using the equation: q = mcΔT
   q = (mass of water) x (specific heat capacity of water) x (change in temperature)
   q = 52.0 g x 4.184 J/g°C x (-9.63 °C) = -2022.66 J
2. Convert the heat from joules to kilojoules:
   -2022.66 J = -2.02 kJ
3. Calculate the moles of KCN using its molar mass:
   Molar mass of KCN = 39.10 g/mol (K) + 12.01 g/mol (C) + 14.01 g/mol (N) = 65.12 g/mol
   moles of KCN = (mass of KCN) / (molar mass of KCN) = 15.00 g / 65.12 g/mol = 0.230 mol
4. Calculate ΔH using the equation: ΔH = q / moles of KCN
   ΔH = -2.02 kJ / 0.230 mol = -8.78 kJ/mol

Therefore, the ΔH for the reaction is -8.78 kJ/mol.