Without doing any calculations, determine the signs of ΔS_sys and ΔS surr for each chemical reaction. In addition, predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reaction is spontaneous. a. C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g) ΔH°_rxn = -2044 kJ

Key Concepts

Entropy (ΔS)

Entropy, represented as ΔS, is a measure of the disorder or randomness in a system. In chemical reactions, an increase in the number of gas molecules or a transition from a solid to a liquid or gas typically results in a positive ΔS, indicating greater disorder. Conversely, reactions that produce fewer gas molecules or involve the formation of solids from gases usually have a negative ΔS.

Enthalpy (ΔH) and Spontaneity

Enthalpy change (ΔH) reflects the heat absorbed or released during a reaction. A negative ΔH indicates an exothermic reaction, which tends to favor spontaneity. The spontaneity of a reaction can be assessed using Gibbs free energy (ΔG = ΔH - TΔS), where a negative ΔG indicates a spontaneous process. The interplay between ΔH and ΔS is crucial in determining the conditions under which a reaction is spontaneous.

Temperature's Role in Spontaneity

Temperature plays a significant role in determining the spontaneity of a reaction, particularly when considering the signs of ΔH and ΔS. At high temperatures, reactions with positive ΔS may become spontaneous even if ΔH is positive, as the TΔS term can outweigh ΔH. Conversely, at low temperatures, reactions with negative ΔS may be spontaneous if ΔH is sufficiently negative, highlighting the importance of temperature in the Gibbs free energy equation.