열용량과 비열. 중화열

열용량과 비열. 중화열

 

 

A quantity of 200 mL of 0.862 M HCl is mixed with 200 mL of 0.431 M Ba(OH)2 in a constant pressure calorimeter that has a heat capacity of 453 J/℃. The initial temperature of the HCl and Ba(OH)2 solution is the same at 20.48 ℃. For the process H+(aq) + OH-(aq) → H2O(l) the heat of neutralization is –56.2 kJ/mol.

What is the final temperature of the mixed solution?

Assume the density of the solution is the same as that of water (1.00 g/mL), and the specific heat of the solution is the same as that for pure water (4.184 J/g•℃).

 

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0.862 mol/L × 0.200 L

= 0.1724 mol HCl = 0.1724 mol H+

 

0.431 mol/L × 0.200 L

= 0.0862 mol Ba(OH)2 = 0.1724 mol OH-

Ba(OH)2(aq) → Ba2+(aq) + 2OH-(aq)

 

H+(aq) + OH-(aq) → H2O(l)

H+ : OH : H2O = 1 : 1 : 1 이므로,

생성된 H2O의 몰수 = 0.1724 mol H2O

 

중화열 = (-56.2 kJ/mol) × 0.1724 mol

= -9.689 kJ = -9689 J

 

계가 방출한 9689 J 열을

주위인 열량계와 물이 나눠 흡수하므로,

 

9689 J = q_열량계 + q_물

= C•Δt + C•m•Δt

= Δt • [C + C•m]

= Δt • [453 J/℃ + (4.184 J/g•℃)(400 g)]

= Δt • 2127 J/℃

 

Δt = (9689 J) / (2127 J/℃) = 4.56 ℃

 

따라서 최종 온도는

20.48 ℃ + 4.56 ℃ = 25.04 ℃

 

답: 25.04 ℃