CHEMISTRY HOMEWORK

Question

In a constant‑pressure calorimeter, 60.0 mL of 0.340 M Ba(OH)2 was added to 60.0 mL of 0.680 M HCl. The reaction caused the temperature of the solution to rise from 22.66 ∘C to 27.29 ∘C. If the solution has the same density and specific heat as water ( 1.00 g/mL and 4.184J/g⋅°C,) respectively), what is Δ𝐻 for this reaction (per mole H2O produced)? Assume that the total volume is the sum of the individual volumes.

Answer 1

Ba(OH)₂ + 2HCl ==> BaCl₂ + 2H₂O ... balanced equation

Total volume = 60.0 ml + 60.0 ml = 120 ml

Mass = 120 ml x 1 g/ml = 120 g

∆T = change in temp = 4.63º

C = specific heat = 4.184 J/gº

q = mC∆T

plug in values and solve for q which is the heat generated by the reaction = ∆H

To get ∆H/mol H₂O look at the balanced equation and solve for moles H₂O produced. You do this by finding moles Ba(OH)₂ and moles HCl present and see how much H₂O can be produced.

Answer 2

Hello, Basia,

I agree with J.R.S's response. I had made my way through the problem before I saw his response. I was originally wondering whether the production of H2O as part of the reaction might through off the calculation, since it is based on the amount of water present. Because so little of the reactants are used, the amount of water produced is 0.7 ml, small with respect to the 120 ml we start with, but still a factor. However, the problem states that we should assume the total is the sum of individual volumes, so I assume this small change was not something that was considered important or relevant.

Remember to keep the units in the calculations. ∆T in this equation is Initial - Final temperatures. This results in a negative value, but don't let that throw you off. The sign indicates which direction the energy is moving. A negative value means energy is being released by the system (the reaction).

Bob