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16 Ιαν 2023 · Example \(\PageIndex{1}\): Entropy Change for a Gas Expansion. Calculate the entropy change for 1.00 mol of an ideal gas expanding isothermally from a volume of 24.4 L to 48.8 L.
- 19.4: Entropy Changes in Chemical Reactions - Chemistry LibreTexts
The entropy change in a chemical reaction is given by the...
- 20.1: Entropy - Chemistry LibreTexts
These examples serve to illustrate how the entropy change in...
- 19.4: Entropy Changes in Chemical Reactions - Chemistry LibreTexts
The entropy change in a chemical reaction is given by the sum of the entropies of the products minus the sum of the entropies of the reactants.
These examples serve to illustrate how the entropy change in a reaction can be predicted: \(\ce{Cl_2} \left( g \right) \rightarrow \ce{Cl_2} \left( l \right)\) The entropy is decreasing because a gas is becoming a liquid.
The equation to calculate the standard entropy change of a system is: ΔSsystemꝋ = ΣSproductsꝋ - ΣSreactantsꝋ. (where Σ = sum of) For example, the standard entropy change for the formation of ammonia (NH 3) from nitrogen (N 2) and hydrogen (H 2) can be calculated using this equation. N2(g) + 3H2(g) ⇋ 2NH3(g)
The equation to calculate the standard entropy change of a system is: ΔS system ꝋ = ΣΔS products ꝋ - ΣΔS reactants ꝋ (where Σ = sum of) For example, the standard entropy change for the formation of ammonia (NH 3) from nitrogen (N 2) and hydrogen (H 2) can be calculated using this equation N 2 (g) + 3H 2 (g) ⇋ 2NH 3 (g)
For chemical reactions, the change in entropy formula is: \small \Delta S_ {\text {reaction}} = \Delta S_ {\text {products}} - \Delta S_ {\text {reactants}} ΔS reaction = ΔS products − ΔS reactants. Entropy (S) is normally measured in J / K, but standard entropy (S o) is also used. This value is measured at 298.15 K and at a pressure of 1 bar.
This page looks at how you can calculate entropy changes during reactions from given values of entropy for each of the substances taking part.
