ASRJC H2 Chem 5b. Thermodynamics

2024 JC1 H2 CHEMICAL ENERGETICS II (THERMODYNAMICS) 2024/ASRJC/Chemistry 1 Anderson Serangoon Junior College H2 Chemistry CHEMICAL ENERGETICS II (THERMODYNAMICS) Contents/Outline 1 Introducing spontaneous process 2 Defining entropy and explaining the factors affecting entropy of a chemical system 3 Predicting the spontaneity of a reaction using Gibbs Free Energy Change 4 Determining the effect of temperature on the spontaneity of a reaction Learning Outcomes Students should be able to: (a) explain and use the term entropy. (b) discuss the effects on the entropy of a chemical system by the following: (i) change in temperature (ii) change in phase (iii) change in the number of particles (especially for gaseous systems) (iv) mixing of particles [quantitative treatment is not required] (c) predict whether the entropy change for a given process or reaction is positive or negative (d) define standard Gibbs free energy change of reaction by means of the equation ∆G = ∆H − T∆S (e) calculate ∆G for a reaction using the equation ∆G = ∆H − T∆S [the calculation of standard entropy change, ∆S, for a reaction using standard entropies, S, is not required] (f) state whether a reaction or process will be spontaneous by using the sign of ∆G (g) predict the effect of temperature change on the spontaneity of a reaction, given standard enthalpy and entropy changes References 1. Chemistry for Advanced Level, Cann and Hughes, Murray 2. Understanding Advanced Physical Inorganic Chemisry, Jeanne Tan and Chan Kim Seng, WS education 3. Chemistry, The Molecular Nature of Matter and Change (Fourth Edition), Silberberg, McGraw Hill 4. Chemistry & Chemical Reactivity (Sixth Edition), Kotz, Treichel and Weaver, Thomson 5. Chemistry The Central Science (Ninth Edition), Brown, LeMay, Bursten, Prentice Hall

2024 JC1 H2 CHEMICAL ENERGETICS II (THERMODYNAMICS) 2024/ASRJC/Chemistry 2 1 SPONTANEOUS PROCESS • What is a spontaneous process? • Can an endothermic reaction be spontaneous? The main objective of studying chemical thermodynamics is to be able to predict whether a reaction is spontaneous. A spontaneous process is one that takes place without any outside interference i.e. takes place by itself without an ongoing input of energy from outside the system. It occurs in a definite direction. Spontaneous reactions can be fast or slow. Slow spontaneous reactions can include ripening, rusting and aging. A spontaneous change is irreversible as it cannot be brought back to its original state unless some outside influence is introduced. Some examples of spontaneous reactions: • A lump of sugar dissolves spontaneously in a cup of coffee but dissolved sugar does not spontaneously reappear in the original form. • Iron exposed to water and oxygen forms rust but rust does not spontaneously change back to iron. • The expansion of a gas in an evacuated bulb is a spontaneous pr