The enthalpy of vaporization for a substance is significantly larger than the en

Question

The enthalpy of vaporization for a substance is significantly larger than the enthalpy of fusion because vapor pressure decreases and boiling point increases as vaporization occurs. temperature remains constant during vaporization but not during melting. to form a vapor, all intermolecular forces must be overcome. the vapor occupies more volume than the liquid. The phase diagram for a substance is shown Proceeding from points 1 to 2 to 3, the substance undergoes the processes of___and___. respectively. condensation, fusion vaporization, deposition sublimation, fusion freezing, vaporization At normal pressure, how much heat must be added to 75.3 g of liquid water at 27.0 degree C to convert all the liquid water to steam at 100.0 degree C? 193 KJ 171 KJ 48.1 KJ 23.0 KJ CaF_2 has K_ap = 3.5 times 10^-11, What is the molar solubility of CaF_2? 6.2 times 10^-6 M 2.1 times 10^-4 M 2.7 times 10^-4 M 3.4 times 10^-4 M In which solution is PbBr_2 least soluble? 0.100 M NaNO_3 0.100 M HBr 0.100 M NaBr 0.100 M MgBr_2 Which aqueous solution has the highest normal boiling point? 0.1 m C_2 H_5 OH 0.1 m NaCI 0.1 m K_3 PO_4 They all have the same boiling point.

Explanation / Answer

51) In case of gases the molecules are need to be separated far from each other as compared to liquids however the intermolcular difference between liquids and solids is comparable.

so to overcome all the forces large amount of heat is required (option C)

52) the area (1) is of vapours area (2) is of liquid and area (3) of solid

from 1 to 2 : condensation

from 2 to 3: fusion

53) Heat required to heat the water sample to 100 C = Q1

Q1= mass X specific heat X change in temperature = 75.3 X 4.18 X (100-27) = 22977.042 Joules = 22.977 KJ

Heat required to change water to steam = Mass of water X heat of vapourisation

Q2 = 75.3 X 2261 = 170253.3 Joules = 170.253 KJ

Total heat = Q1 + Q2 = 22.977 + 170.253 = 193.23KJ

54) Ksp = [Ca+] [ F-]^2

Let solubility of CaF2 = x

Ksp = 3.5 X 10^-11 = [x][2x]^2 = 4x^3

x = 2.06 X 10^-4

55) The salt will be least soluble in the solution containing largest concentration of common ion

concentration of Br- in MgB2 = 0.2 M

so it will least soluble in MgBr2

56) The normal boiling point increases with increase in number of ions of solute

so in 0.1m K3PO4 (4 ions)

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