Calculating Heat Required

Nick Foucrier 3J
Posts: 20
Joined: Sat Jul 09, 2016 3:00 am

Calculating Heat Required

On page 19 in the course reader, we are given a formula such that Qp=n*Cp*change in temperature. Written on the board was the formula Q=(mass)*Csp*change in temperature. I am confused as to what the difference between these equations are and when to use each one. Please help!

Rachel Kipp 1I
Posts: 16
Joined: Wed Sep 21, 2016 2:55 pm

Re: Calculating Heat Required

Note the Qp and just the Q in the second equation. The first equation takes into account constant pressure, while Q in the second equation is heat that is not at constant pressure.

Navarro_Bree_1D
Posts: 24
Joined: Wed Sep 21, 2016 3:00 pm

Re: Calculating Heat Required

Although these heat equations look very similar, they are quite different.

1. Qp=n*Cp*change in temperature
2. Q=(mass)*Csp*change in temperature

For the first equation,
-heat is at constant pressure
-n = # of moles
-Cp = molar heat capacity at constant pressure (kJ/C mol)
-you use moles to cancel out the mole in Cp

For the second equation,
-heat is NOT at constant pressure
-mass = amount of substance in grams
-Csp = specific heat capacity (kJ/C g)
-you use grams to cancel out the gram in Csp

Hope this helps!

Ashley Shirriff 2F
Posts: 10
Joined: Wed Sep 21, 2016 2:55 pm

Re: Calculating Heat Required

I understand the meanings behind each component within the equations; however I am still unsure as to how you know when to use which one. I assumed that if the problem states that, for example, there is constant pressure and gives the amount of the substances involved in moles then you would use molar heat capacity. But the example provided in the course reader gives constant p and molar values yet uses specific heat capacity to solve the problem. Could somebody explain this to me?