Question

Suppose that coal of density 1.5g/cm3 is pure carbon. The combustion of carbon is described by the equation
C+O2---> CO2 ∆H◦ = −394 kJ
What is the value of q (heat) a ump of coal the size of 7.5cm*7cm*6.5cm is burned? answer in kJ

what mass of water can be heated from 25C to 100C by burning this piece of coal? Answer in grams

Answer 1

volume coal = 7.5*7*6.5 = aprox 340 cc
mass = volume x density = approx 500g but you should recalculate this number and all of the others that follow because I've estimated all of them.
?kJ = apprx 394 kJ x (500/12) = ? and it is exothermic so it has a - sign.
Then
+q = [mass H2O x specific heat H2O x
(Tfinal-Tinitial)]
Substitute and solve for mass H2O

Answer 2

What is the specific heat? And tfinal and tinitial?

Answer 3

The specific heat of H2O should be listed in your text but I think it is 4.184 J/g*c.
Tfinal is listed in the problem as 100 C.
Tinitial is listed in the problem as 25 C.
Note that if you use specific heat in J/g*c you must change q from the first part of the problem from kJ to J and substitute J in the second part of the problem to solve for mass H2O. I ran through the problem quickly and the answer is in the vicinity of 50 g H2O for the second part and about -17 kJ for the first part. Remember to change the sign to + for the second part.