Part A - Calculating ΔS∘ from Tabulated Entropies Using the standard molar entropies below, calculate the standard entropy change, ΔS∘ , for the "water-splitting" reaction at 298 K: 2H2O(l) → 2H2(g) + O2(g) Standard Molar Entropies of Selected Substances at 298 K Substance S∘ (J/mol⋅K) H2(g) 130.6 O2(g) 205.0 H2O(g) 188.8 H2O(l) 69.9 Using the standard molar entropies below, calculate the standard entropy change, , for the "water-splitting" reaction at 298 : Standard Molar Entropies of Selected Substances at 298 Substance () 130.6 205.0 188.8 69.9 326.4 J/K 265.7 J/K 163.2 J/K 88.5 J/K −326.3 J/K

The standard entropy or reaction ΔS° =+324.6J/mol.K

Explanation:

The reaction is

2H2O(l) → 2H2(g) + O2(g)

Standard Molar Entropies of Selected Substances at 298 K are

SubstanceS∘ (J/mol⋅K)

H2(g)130.6

O2(g)205.0

H2O(g)188.8

H2O(l)69.9

The standard entropy of reaction will be obtained from standard entropy of formation as given below

ΔH°= 2(130.6)+(205.0)-2(69.9) (Jol/mol.K)

ΔH°=261.2+205.0-139.8

ΔH°=+324.6Jol/mol.K

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.