(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

1) How much heat energy must be added to the gaseous mixture consisting of 1 gm of Hydrogen and 1 gm of Helium to raise its temperature from 0 degree C to 100 degree C

at constant pressure? Given that g1=1.41, g2=1.67

2. Relevant equations

Heat required = nC(p)dT

3. The attempt at a solution

Heat energy in Joules:

Let C(p1), C(p2) and C(p) be the specific heat of Hydrogen, Helium and the mixture at constant pressure respectively. Let g1,g2 and g be the ratio of the specific heats at constant volume and pressure for Hydrogen, Helium and the mixture respectively. Here I have taken the value of the universal Gas constant[R] = 8.314 Joule/mole-K

C(p1) = (g1 x R)/(g1 -1)

= 28.59 J/mole-K

C(p2) = (g2 x R)/(g2-1)

= 20 .72 J/mole-K

C(p) = {(n1 x C(p1)) + (n2 x C(p2))}/(n1 + n2)

= 709.7 J/mole-K

Let n1,n2 and n be the number of moles of Hydrogen, Helium and the mixture respectively.

n1 = 0.5 moles

n2 = 0.25 moles

n = 0.75 moles

Heat required = nC(p)dT

= 53200 Joules = 12666 Calories

Heat energy in Calories:

Here I have taken the value of the universal Gas constant[R] = 1.99 Calorie/mole-K

Heat required = 466 Calories

Why do I get 2 different answers just because of change in units of R?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Heat required at constant pressure

**Physics Forums | Science Articles, Homework Help, Discussion**