petewil2009
Sep13-10, 08:36 AM
1. The problem statement, all variables and given/known data
At 25C Cu metal (at. wt. 63.54 g/mol) has a molar heat capacity of 24.4 J/molK. The density of Cu is 8.949g/cm^3 at 0C and 8.904 g/cm^3 at 100C. Assuming that Cp is temperature independent, calculate Q, W, deltaU and deltaH when 100grams of Cu metal are heated from 0C to 100C under constant pressure 1atm.
Ans. Q=deltaH is about equal to deltaU = 3840J, W=-.0057J
Note: deltaH is about equal to deltaU for heating of solids and liquids at constant pressure because these materials exhibit very low volume changes on heating.
3. The attempt at a solution
density = m/v so v=m/density so
V1=100g/8.949g/cm^3 = 11.17cm^3 and V2 = 100g/8.904 g/cm^3 = 11.23cm^3
W=-P(V2-V1) = -1atm((11.23X10^-2(m^3))-(11.17X10^-2(m^3)))=-.0006J about correct?
Q=nCn(Tf-Ti)
n=((63.54g/mol)/(100g))=.6354mol
Q = (.6354mol)(24.4J/molK)(373K) = 5782.9J not so correct?...
At 25C Cu metal (at. wt. 63.54 g/mol) has a molar heat capacity of 24.4 J/molK. The density of Cu is 8.949g/cm^3 at 0C and 8.904 g/cm^3 at 100C. Assuming that Cp is temperature independent, calculate Q, W, deltaU and deltaH when 100grams of Cu metal are heated from 0C to 100C under constant pressure 1atm.
Ans. Q=deltaH is about equal to deltaU = 3840J, W=-.0057J
Note: deltaH is about equal to deltaU for heating of solids and liquids at constant pressure because these materials exhibit very low volume changes on heating.
3. The attempt at a solution
density = m/v so v=m/density so
V1=100g/8.949g/cm^3 = 11.17cm^3 and V2 = 100g/8.904 g/cm^3 = 11.23cm^3
W=-P(V2-V1) = -1atm((11.23X10^-2(m^3))-(11.17X10^-2(m^3)))=-.0006J about correct?
Q=nCn(Tf-Ti)
n=((63.54g/mol)/(100g))=.6354mol
Q = (.6354mol)(24.4J/molK)(373K) = 5782.9J not so correct?...