Hydrochloric acid reacts with barium hydroxide according to the equation:
Calculate the heat (in kJ)associated with the complete reaction of 18.2 grams of HCl (aq).

Question

Hydrochloric acid reacts with barium hydroxide according to the equation: 
Calculate the heat (in kJ)associated with the complete reaction of 18.2 grams of HCl (aq).

Quizplus · Accepted Answer

Firstly, we need to convert the mass of HCl to moles:

18.2 g HCl x 1 mol HCl/36.46 g HCl = 0.499 mol HCl

According to the equation, 2 moles of HCl reacts with 1 mole of Ba(OH)2. Therefore, the number of moles of Ba(OH)2 required for the reaction is:

0.499 mol HCl x 1 mol Ba(OH)2/2 mol HCl = 0.2495 mol Ba(OH)2

Now, using the molar mass of Ba(OH)2, we can convert the amount of Ba(OH)2 from moles to grams:

0.2495 mol Ba(OH)2 x 171.34 g Ba(OH)2/mol = 42.778 g Ba(OH)2

We can use the equation q = mCΔT to calculate the heat (q) produced by the reaction. We need to know the mass of water and the change in temperature. Assuming the reaction takes place in a dilute solution of HCl and Ba(OH)2, we can assume a specific heat capacity of 4.184 J/g°C for the solution. We can also assume that the reaction is exothermic, so the temperature of the solution will increase.

The mass of water can be calculated from the mass of HCl, using the assumption that the solution has a density of 1.00 g/mL:

18.2 g HCl + m water = 18.2 mL solution
m water = 18.2 g - (18.2 mL - 42.778 g) = 18.2 g - 24.578 g = -6.378 g

This negative value means that we need to add 6.378 g of water to the 18.2 g of HCl to make a 24.578 g solution.

The change in temperature can be calculated from the enthalpy change (ΔH) of the reaction:

ΔH = -1020 kJ/mol Ba(OH)2 (from the equation)
ΔH = q/n (where n is the number of moles of Ba(OH)2)

q = nΔH
q = 0.2495 mol Ba(OH)2 x (-1020 kJ/mol Ba(OH)2) = -254.19 kJ

Now we can calculate the change in temperature:

q = mCΔT
-254.19 kJ = (18.2 g + 6.378 g) x 4.184 J/g°C x ΔT
ΔT = -3.66°C

Since the temperature decreases, the reaction must be endothermic. Therefore, the answer is C) -29.5 kJ.

Hydrochloric Acid Reacts with Barium Hydroxide According to the Equation