Question

The balanced combustion reaction for CH is 2CH.(1) + 150,(g) — 12 CO2(g) + 6H,0(1) + 6542 kJ If 8.500 g C, H, is burned and the heat produced from the burning is added to 5691 g of water at 21 C, what is the final temperature of the water? final temperature:

Answer 1

Molar mass of C6H6,

MM = 6*MM(C) + 6*MM(H)

= 6*12.01 + 6*1.008

= 78.108 g/mol

mass(C6H6)= 8.500 g

use:

number of mol of C6H6,

n = mass of C6H6/molar mass of C6H6

=(8.5 g)/(78.11 g/mol)

= 0.1088 mol

Since Δ H is negative, heat is released

when 2 mol of C6H6 reacts, heat released = 6542.0 KJ

So,

for 0.1088 mol of C6H6, heat released = 0.1088*6542.0/2 KJ

= 356.0 KJ

This heat is absorbed by water

Given:

Q = 356000 J

m = 5691 g

C = 4.184 J/g.oC

Ti = 21 oC

use:

Q = m*C*(Tf-Ti)

356000 = 5691*4.184*(Tf-21.0)

Tf -21.0 = 15.0 oC

Tf = 36.0 oC

Answer: 36.0 oC