Thermodynamics is one of the big ideas in chemistry, If youre wondering whether

Question

Thermodynamics is one of the big ideas in chemistry, If youre wondering whether a criminal ction will occur spontaneously, or why a reaction occurs, the answer corners energetics of the system. (Other ideas that answer big questions are equilibrium the question to what extent a reaction will occur, and kinetics, which answers the quo down , which answers of "how fast" a reaction will occur.) Part I: Concept Review 1. For each process belowpredict the sign , , as, and of AHAG, indicate whether the spontaneity of the process depends on temperature. Describe your reasoning in each case. In some cases, you may need state what additional information is order to to make prediction needed in a . a. 20(9) - O2(g) Short explanation: Prediction: AH: - 0 + AS: 0 + AG : - 0 + T dependent? B. Dissolving CaClk(s) in water (feels warm) Short explanation: Prediction: AH. - 0 + AS: AG : - 0 + T dependent? c. 2HF(g) H2(g) + Falg) Short explanation: Prediction: AH: - 0 + AS: -0+ AG: - 0 + T dependent? d. Making ice cubes Short explanation: Prediction: AH: - 0 + AS AG: + T dependent? : - AGCO Short explanation: • , :: Prediction: AH: AS: AG: - 0 + T dependent? "What is the relationship between "a" and "e"?

Explanation / Answer

Q1

a)

bonds are formed, therefore exothermic, dH = negative

2 molecules of O --> 1 molecules of O2 decrease in entropy, dS = negative

dG = dH - T*dS

dG = negative - T* (negative) will only be valid at T low

b)

CaCl2(s) --> Ca+2 + 2Cl-

dissolution increases chaos, i.e. orderer water + lattice will form disordered ions in solution

if feels warm, the reactino is exothermic

so

dH = negative, dS = positive

always favoured, i.e. T independent

c)

H-F break to form H2, F2

130.7+ 202.8 - (2*173.8) = -14.1 , entorpy decreases

Hf = -273.3*2 - (0) = -546.6

this has negative enthalpy and negative entropy

dS = negative, dH = negative, so

dG = dH - T*dS

T must be high

d)

making ice cubes

enthalpy --> heat is released, so exothermic, dH = negative

entropy --> liquid > solid, so the entorpy decreases

dH = negative, dS = negative, only possible at low T

e)

inverted as in a,

complex molecules form singl moleucles --> S increases

H = positive

dG = dH - T*dS

dG = positive - T*positive

must be high T

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