The enthalpy of vaporization for a substance is significantly larger than the en
ID: 993195 • Letter: T
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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 vapourization 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 points1 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 753 g of liquid water at 27.0 degrees C to convert all the liquid water to steam at 100.0 degrees C? 193 kJ 48.1 kJ 171 kJ 23.0 kJ CaF_2 has K_tp= 3.5 times 10^minus 11. What is the molar solubility of CaF_2? 6.2 times 10^minus 6 M 2.1 times 10^minus 1M 2.7 times 10^minus 1M 3.4 times 10^minus 1M 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 highrit normal boiling point? 0.1 m C_2H_5OH 0.1 m NaCl 0.1 m K_4PO_4 They all have the same boiling point.Explanation / Answer
(1) We know that in solids the particles are very close enough. When we move from solid to liquid then particles are going away from one another. there is not like much difference in the spacing between solids and liquid but if we talk about the gas (vapor) then particles(molecules) are very far away and we know that it always needs energy to move them away. This is the main reason why enthalpy of vaporization is significant larger than enthalpy of fusion.
When particles are at longer distance then attraction forces takes place between them. So, to over come these attraction forces (intermolecular forces) we need to supply more energy. So, the correct choice is (C).
(2) High pressure and low temperature support the solid phase since at lower temperature molecules have east kinetic energy and at high pressure they are closest. Point 3, is along the pressure axis and there is like high pressure and low temperature, so there would be like solid phase. Point 2, Here the pressure is least and temperature is high so it must be a gas phase. Point 1, here both pressure and temperature are high so it would be the liquid phase.
So, it is coming from point 1 to 2, liquid is changing into vapor so we call it vaporization curve. From point 2 to 3, vapor is changing into solid (ice) so it is deposition curve.
hence, the correct choice is (B). Vaporization, deposition.
(3) if we want to convert 27.0 degree liquid water into 100.0 degree steam then it would be two step process.
In first step, 27.0 degree C water will change into 100.0 degree C water. for this step...
q = m c delta T
where, q is heat energy, m is mass, c is specific heat capacity and delta T is change in temperature.
delta T = 100.0 - 27.0 = 73.0 degree C
q = 75.3 g x 4.184 J/(g x C) x 73.0 = 22999.0296 J
in second step, 100.0 degree C water will change into 100.0 degree C steam. For this step..
q = m x delta Hvap
q = 75.3 g x 2261 J/g = 170273.3 J
Total energy = 22999.0296 J + 170273.3 J = 193252.3296 J Or approx 193 kJ ( since 1000 J = 1 kJ)
So, the correct choice is (A) 193 kJ
(4) CaF2(s) ------------> Ca+2(aq) + 2F-(aq)
Ksp = [Ca+2(aq)] [F-(aq)]2
let's say the molar solubility of CaF2 is X. then Ca+2(aq) would be X and F- would be 2X. (since there is 1:2 mol ratio between CaF2 and F-)
3.5 x 10-11 = (X) (2X)2 = 4X3
X3 = 3.5 x 10-11/4 = 8.75 x 10-12
taking cube root on both sides....
X = 2.06 x 10-4
It means the molar solubility is 2.06 x 10-4M and it could be round to 2.1 x 10-4M. So, the correct choice is (B).
(5) Here we consider common ion effect. The solubility decreases due to common ion effect. amoungts the given choices, HBr, NaBr and MgBr2. since concentartions are same for all of them but MgBr2 gives two Br- ions hence the the solubility of PbBr2 would be least in MgBr2.
(6) Elevation in boling point, delta Tf = i x m x Kf
where i is Van't hoff cator, a theoretical number of particles that we get when an ionic compound breaks and Kf is a constant and m is molality. Kf and m are same for all of them. so, all it depends on i here.
since K3PO4 gives 4 ions hence i = 4, and so the boiling point would be greatest for it. The correct choice is (C)
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