Heat of reaction in constant pressure calorimeter (Chemistry)

[mwamba]

Homework Statement

A 30.0mL sample of 0.937M A is mixed with 16.7mL of 0.904M B in a constant pressure calorimeter. The thermochemical equation for this reaction is:
A(aq) + B(aq) --> C(aq) + D(aq); ΔH = 41.2kJ

Both solutions are at 24.9 degrees Celsius prior to mixing and reacting. What is the final temperature of the reaction mixture? The density of all solutions is 1.00 g/mL and the specific heat is 4.184 J/gC.

Homework Equations

q = mcΔT where m is mass, c is specific heat and ΔT is the change in temperature.

The Attempt at a Solution

q = (30mL + 16.7mL) * 1.00g/mL * 4.184 J/gC * (xC - 24.9C) where C stands for Celsius and x is the final temperature (what we want to find).

Finding limiting reagent:
?mL A = 16.7mL B * (1L/1000mL) * ((0.904mol B)/1L) * ((1mol A)/0.937)*1000mL
= 16.11mL A < 16.7mL B so B is the limiting reagent

Finding q:
41200J = 1mol B * qJ/0.0151
q = 622.12J

Substituting q into the original equation to find x:


622.12J = (30mL + 16.7mL) * 1.00g/mL * 4.184 J/gC * (xC - 24.9C)
x = 28.1 degrees Celsius

This is apparently wrong. The answer is supposed to be 21.7 degrees Celsius. Does anyone see where I went wrong?

 

[Borek]

Sign. Is the reaction exothermic (temperature goes up) or endothermic (temperature goes down)?