Calculate S (measure of total entropy) for the following reaction at 25C and 1atm, and tell whether the entropy is increasing or decreasing.
C3H8(g)+5O2(g)-> 3CO2(g)+4H2O(g)
S of C3H8=64.5 cal/(mol*K)
S of O2= 49 cal/(mol*K)
S of CO2= 51.1 cal/(mol*K)
S of H2O= 45.1 cal/(mol*K)
S of the equation is 23.9 and increasing entropy.
I do not know how to factor in the temp. and atm... please help!!!
Is this just
Srxn = Sproducts-Sreactants.
And if you look them in a table, that is at 25 C and 1 atm isn't it.
To calculate the change in entropy (ΔS) for the given reaction at 25°C and 1 atm, you need to use the formula:
ΔS = Σ(n * S_products) - Σ(m * S_reactants)
where:
- Σ means summation or sum of the terms
- n and m represent the balanced coefficients of the products and reactants, respectively
- S_products and S_reactants represent the molar entropies of the products and reactants, respectively.
Let's calculate step-by-step:
1. Determine the balanced coefficients of the products and reactants:
C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(g)
2. Calculate the entropy change for the products:
Σ(n * S_products) = 3 * 51.1 + 4 * 45.1
3. Calculate the entropy change for the reactants:
Σ(m * S_reactants) = 1 * 64.5 + 5 * 49
4. Calculate the change in entropy (ΔS):
ΔS = [Σ(n * S_products)] - [Σ(m * S_reactants)]
Calculate the values:
Σ(n * S_products) = (3 * 51.1) + (4 * 45.1) = 153.3 + 180.4 = 333.7 cal/(mol*K)
Σ(m * S_reactants) = (1 * 64.5) + (5 * 49) = 64.5 + 245 = 309.5 cal/(mol*K)
ΔS = 333.7 - 309.5 = 24.2 cal/(mol*K)
The change in entropy (ΔS) for this reaction is 24.2 cal/(mol*K). Since the value is positive, the entropy is increasing.
To calculate the total entropy change (S) for the given reaction, we need to use the entropy values (S) of the reactants and products. The formula for calculating the change in entropy (ΔS) is:
ΔS = ΣS(products) - ΣS(reactants)
First, we'll calculate the entropy change for the products:
ΣS(products) = (3 × S(CO2)) + (4 × S(H2O))
= (3 × 51.1 cal/(mol*K)) + (4 × 45.1 cal/(mol*K))
Next, we'll calculate the entropy change for the reactants:
ΣS(reactants) = S(C3H8) + (5 × S(O2))
= 64.5 cal/(mol*K) + (5 × 49 cal/(mol*K))
Now, we can calculate the total entropy change:
ΔS = ΣS(products) - ΣS(reactants)
= [(3 × 51.1 cal/(mol*K)) + (4 × 45.1 cal/(mol*K))] - [64.5 cal/(mol*K) + (5 × 49 cal/(mol*K))]
To factor in the temperature and pressure in the entropy calculations, we need to know the standard state ΔSº values instead of the given entropy values at specific conditions (25°C and 1 atm). The standard state values are measured at 298 K (25°C) and 1 atm pressure. But for the purpose of this explanation, we'll proceed with the given values.
Calculating the above expression gives:
ΔS = (153.3 cal/(mol*K)) - (263.5 cal/(mol*K))
= -110.2 cal/(mol*K)
The calculated ΔS value is -110.2 cal/(mol*K), indicating a decrease in entropy.
Therefore, the total entropy change (S) for the given reaction at 25°C and 1 atm is -110.2 cal/(mol*K), and the entropy is decreasing.