I posted this question already but you never replied back :(
Consider the following reaction at 298 K:
C(graphite) +2Cl2 (g) -----> CCl4(l)
Calculate the following quantities.
Delta H: -139 kJ/mol
deltaS(sys)=? J/mol*K
deltaS(surr)=? J/mol*K
deltaS(univ)=? J/mol*K
My answer is:
deltaS(sys)=-253.3J/mol*K
deltaS(surr)=466.4 J/mol*K
deltaS(univ)=231.4 J/mol*K
Delta (surr) and (univ) are correct. But delta (sys) is wrong...please help thanks!
chemistry - DrBob222, Friday, March 16, 2012 at 11:38pm
How did you calculate the dS sys? What values did you use?
chemistry - Leila, Saturday, March 17, 2012 at 2:40pm
Change in Hf(kJ/mol) Change in G Change in S
C(graphite) 0 0 5.7
Cl2 0 0 223.1
CCl4 -139 -68.6 214.4
************The values I used
C(graphite):
change in delta Hf=0
change in delta G= 0
change in delta S= 5.7
Cl2
change in delta Hf=0
change in delta G= 0
change in delta S= 223.1
CCl4
change in delta Hf=-139
change in delta G= -68.6
change in delta S= 214.4
The values above are in the units of kJ/mol
never mind I subtracted wrong the answer is -235.4 hahaha
To calculate the deltaS(sys), you need to use the change in entropy values for each species involved in the reaction. The change in entropy values can be found from tables or calculated using the formula:
deltaS = n * deltaS°(products) - m * deltaS°(reactants)
Where:
- deltaS is the change in entropy
- n and m are the stoichiometric coefficients of the products and reactants
- deltaS° is the standard entropy change for each species
Using the values you provided, the calculation for deltaS(sys) can be done as follows:
deltaS(sys) = (1 * 214.4) - (1 * 0 + 2 * 223.1)
= 214.4 – 446.2
= -231.8 J/mol*K
Therefore, the correct value for deltaS(sys) is -231.8 J/mol*K, not -253.3 J/mol*K as stated in your answer.
To calculate deltaS(surr), we can use the equation:
deltaS(surr) = -deltaH(sys) / T
Where:
- deltaH(sys) is the enthalpy change of the system (given as -139 kJ/mol)
- T is the temperature in Kelvin (298 K)
deltaS(surr) = -(-139 kJ/mol) / (298 K)
= 466.4 J/mol*K
Therefore, the value for deltaS(surr) is indeed 466.4 J/mol*K.
Lastly, to calculate deltaS(univ), it can be done using the equation:
deltaS(univ) = deltaS(sys) + deltaS(surr)
deltaS(univ) = -231.8 J/mol*K + 466.4 J/mol*K
= 234.6 J/mol*K
Therefore, the correct value for deltaS(univ) is 234.6 J/mol*K, not 231.4 J/mol*K as stated in your answer.
I hope this helps clarify the calculation and provides you with the correct values for deltaS(sys), deltaS(surr), and deltaS(univ).