1. Calcium oxide, Cao(s, has been proposed substance that can be used to heat wa

Question

1. Calcium oxide, Cao(s, has been proposed substance that can be used to heat water quickly for portable as a equation above. heating packs or for cooking. When placed in water, CaOs) reacts as shown by the (a) A student wants to design a heating pad that could heat a 150.0 g sample of water from 25.0 c to 60.0 c. orb for its temperature to change by this amount. (Assume that the specific heat capacity of the water is 4.18 Jl(g. C).) temperature change. (b) The student hypothesizes that the design of the heating pad could be changed to enable it to heat 150.0 g of water from 25.0°C to 90.0 by using a greater mass of CaO(s). Use the data in the table below to determine the standard entropy change, Asan, in Ju(K.moln for the reaction. Absolute Entropy at Substance CaO(s) 83 H200) 70. 40. Ca(OH)2(s) (iij Is the thermodynamically favorable at 90.00c? Justify your answer with a calculation. reaction (Assume that both AS and AH are constant between 25.0°C and 90.0°C)

Explanation / Answer

1) a) i)

Q=mCpT = 150 gm* 4.18 j/gm 0c * (60-25)0c = 21945 j

ii)

Hreaction = Q=mCpT

Molecular weight of CaO = 56.0774 g/mol

Hreaction = 63.7 kj/mol = 63.7 (kj/mol) / 56.0774 (g/mol) = 1.13 kj/gm

1.13 kj/gm = m * 4.18 j/gm 0c * (60-25)0c

M= 7.75 gm

b) i)

S rex = S product - S reactant

S rex = 40-(83+70) = -113 j/K mol

ii)

G>0, the reaction is nonspontaneous in the forward direction, not thermodynamically favourable

G<0, the reaction is spontaneous in the forward direction, thermodynamically favourable

G=HTS = -63.7* 103(j/mol) – 363* (-113) (j/K mol) =-22681 j/mol

Therefore reaction is favourable.

c)

Ksp=[Ca++] [OH-]2

Given ca++ = 0.011 M

From reaction ,

[OH-] = 2 [Ca++] = 0.022 M

Ksp= 0.011* 0.0222 = 5.324*10-6

d)

Ca(OH)2 --------------> Ca++ + 2 OH-

According to Le Châtelier, the position of equilibrium will shift to counter the changes.

i) addition of distilled water

H2O ------> H+ + OH-

The reaction will shift towards left, & solubility of Ca(OH)2 will decrease

ii) Addition of KOH

KOH --------> K+ + OH-

The reaction will shift towards left, & solubility of Ca(OH)2 will decrease

iii) Addition of CaCl2

CaCl2 ----------------> Ca ++ + 2Cl-

The reaction will shift towards left, & solubility of Ca(OH)2 will decrease

iv) Addition of HCl

HCl -----> H+ + Cl-

No effect on solubility of Ca(OH)2

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