• The Enthalpy Of Vaporization Of Benzene Is 33.9 At 298 Inches
• The Enthalpy Of Vaporization Of Benzene Is 33.9 At 298 Feet

Δ f H° gas: Enthalpy of formation at standard conditions (kJ/mol). Δ f H° liquid: Liquid phase enthalpy of formation at standard conditions (kJ/mol). Δ fus H°: Enthalpy of fusion at standard conditions (kJ/mol). Δ fus H: Enthalpy of fusion at a given temperature (kJ/mol). Δ vap H°: Enthalpy of vaporization at standard conditions (kJ/mol). The molar enthalpy of vaporization of benzene at its boiling pt (353K) is 30.84kJ/mol.What is the molar internal energy change?For how long would a 12 volt source need to supply a 0.5A current in order to vaporize 7.8g of the sample at its boiling pt.?

The Clausius-Clapeyron Equation

I plan to use slighty different formulations of the Clausius-Clapeyron Equation in the first several questions. Look to see how they are different. Why do I do this? As you encounter different presentations, you will probably see whatever form of the equation the instructor (or the textbook writer) learned. There is a decent chance that it will be different from the form you learned. I would like for you to see that they are the same equation. As Ludwig Wittgenstein said:

Understanding means seeing that the same thing said different ways is the same thing.

Some brief notes on the units:

1) The natural log term on the left-hand side is unitless. It does not matter what units of pressure you use; the only restriction is that P₁ and P₂ must be expressed using the same pressure unit.

2) The unit on the temperature term will be K¯¹. The unit on R is J mol¯¹ K¯¹.

3) The K¯¹ in the temperature term will cancel with the K¯¹ associated with R.

4) This means that the unit on ΔH must be J/mol. This then makes the right-hand side unitless.

Below, I plan to just solve a few problems. If you want more on this equation please see here. Or, fire up Teh Great Googlizer.

Problem #1: Determine ΔH_vap for a compound that has a measured vapor pressure of 24.3 torr at 273 K and 135 torr at 325 K.

Solution:

1) Let us use the Clausius-Clapeyron Equation:

with the following values:

Solution:

1) Let us use the Clausius-Clapeyron Equation:

ln (P₁ / P₂) = (ΔH / R) (1/T₂ - 1/T₁)

with the following values:

₂)

ΔH_vap = [-R x ln (P₁/P₂)] / (1/T₁ - 1/T₂)

2) Insert values and solve:

ΔH_vap = [(-8.314 J/mole K) x ln (213 torr / 836 torr)] / (1/313.15 K - 1/353.15 K)

ΔH_vap = 31.4 kJ/mole

Problem #4: The molar enthalpy of vaporization of hexane (C₆H₁₄) is 28.9 kJ/mol, and its normal boiling point is 68.73 °C. What is the vapor pressure of hexane at 25.00 °C?

Solution:

1) Let us use the Clausius-Clapeyron Equation:

ln (P₁ / P₂) = - (ΔH / R) (1/T

The Enthalpy Of Vaporization Of Benzene Is 33.9 At 298 Inches

₁ - 1/T₂)

with the following values:

Problem #6: The normal boiling point of Argon is 83.8 K and its latent heat of vaporization is 1.21 kJ/mol. Calculate its boiling point at 1.5 atmosphere.

Solution:

1) Let us use the Clausius-Clapeyron Equation:

ln (P₁ / P₂) = - (ΔH / R) (1/T₁ - 1/T₂

The Enthalpy Of Vaporization Of Benzene Is 33.9 At 298 Feet

)

with the following values:

P1 = 197 mmHg	T1 = 296 K
P2 = 448 mmHg	T2 = 318 K

2) Set up equation to solve for the enthalpy of vaporization:

ln (197 / 448) = - (x / 8.31447) (1/296 minus 1/318)

x = 29227.66 J = 29.2 kJ

3) Let us use the Clausius-Clapeyron Equation:

ln (P₁ / P₂) = - (ΔH / R) (1/T₁ - 1/T₂)

with the following values:

P1 = 1	T1 = 298 K
P2 = 3	T2 = x

Comment: I don't care what the actual vapor presssure value is at either temperature. I just care that it triples in value from P₁ to P₂. Wy can I do this? Because I will be using a ratio of P₂ to P₁. I only care that that ratio is 3.

3) Set up equation with values:

ln (3/1) = (59110 / 8.31447) (1/298 minus 1/x)

1.0968 = 7109.2926 (1/298 minus 1/x)

1.0968 = 23.8567 minus 7109.2926/x)

x = 312.4 K = 39.4 °C

Clicking this link will take you to a NIST paper that has a table of calculated mercury vapor pressures. See page 20.

Also, notice the kinda, sorta vapor pressure assumption. I assumed that only some of the 3.00 g of Hg evaporated at 25 °C. That's a fair assumption, I would think.

This page provides supplementary chemical data on benzene.

Material Safety Data Sheet[edit]

The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet (MSDS) for this chemical from a reliable source such as SIRI, and follow its directions. MSDS for benzene available at AMOCO.

Structure and properties[edit]

Structure and properties
Refractive index, nD	1.5011 at 20°C
Abbe number	?
Dielectric constant, εr	(2.274 – 0.0020ΔT) ε0 (ΔT = T – 25 °C)
Bond energy	?
Bond length	1.39 Å C-C[1]
Molecular geometry	120°C–C–C 120° H–C–C
Magnetic susceptibility	?
Surface tension	28.88 dyn/cm at 25°C
Viscosity[2]	0.7528 mPa·s at 10°C 0.6999 mPa·s at 15°C 0.6516 mPa·s at 20°C 0.6076 mPa·s at 25°C 0.5673 mPa·s at 35°C 0.4965 mPa·s at 40°C 0.4655 mPa·s at 45°C 0.4370 mPa·s at 50°C 0.4108 mPa·s at 55°C 0.3867 mPa·s at 60°C 0.3644 mPa·s at 65°C 0.3439 mPa·s at 70°C 0.3250 mPa·s at 75°C 0.3075 mPa·s at 80°C

Thermodynamic properties[edit]

Phase behavior
Triple point	278.5 K (5.4 °C), 4.83 kPa
Critical point	562 K (289 °C), 4.89 MPa
Std enthalpy change of fusion, ΔfusHo	9.9 kJ/mol at 5.42 °C
Std entropy change of fusion, ΔfusSo	35.5 J/(mol·K) at 5.42 °C
Std enthalpy change of vaporization, ΔvapHo	33.9 kJ/mol at 25°C 30.77 kJ/mol at 80.1°C
Std entropy change of vaporization, ΔvapSo	113.6 J/(mol·K) at 25°C 87.1 J/(mol·K) at 80.1°C
Solid properties
Std enthalpy change of formation, ΔfHosolid	? kJ/mol
Standard molar entropy, Sosolid	45.56 J/(mol K)
Heat capacity, cp	118.4 J/(mol K) at 0°C
Liquid properties
Std enthalpy change of formation, ΔfHoliquid	+48.7 kJ/mol
Standard molar entropy, Soliquid	173.26 J/(mol K)
Enthalpy of combustion, ΔcHo	–3273 kJ/mol
Heat capacity,[2]cp	134.8 J/(mol K)
Gas properties
Std enthalpy change of formation, ΔfHogas	+82.93 kJ/mol
Standard molar entropy,[3] Sogas	269.01 J/(mol K)
Heat capacity,[2]cp	82.44 J/(mol K) at 25°C
van der Waals' constants[4]	a = 1823.9 L2 kPa/mol2 b = 0.1154 liter per mole

Vapor pressure of liquid[edit]

P in mm Hg		1	10	40	100	400	760	1520	3800	7600	15200	30400	45600
T in °C		–36.7(s)	–11.5(s)	7.6	26.1	60.6	80.1	103.8	142.5	178.8	221.5	272.3	—

Table data obtained from CRC Handbook of Chemistry and Physics 44th ed. Note: (s) notation indicates equilibrium temperature of vapor over solid, otherwise value is equilibrium temperature of vapor over liquid.

Distillation data[edit]

Vapor-liquid Equilibrium for Benzene/Ethanol[5] P = 760 mm Hg BP Temp. °C % by mole ethanol liquid vapor 70.8 8.6 26.5 69.8 11.2 28.2 69.6 12.0 30.8 69.1 15.8 33.5 68.5 20.0 36.8 67.7 30.8 41.0 67.7 44.2 44.6 68.1 60.4 50.5 69.6 77.0 59.0 70.4 81.5 62.8 70.9 84.1 66.5 72.7 89.8 74.4 73.8 92.4 78.2

Vapor-liquid Equilibrium for Benzene/Methanol[5] P = 760 mm Hg BP Temp. °C % by mole methanol liquid vapor 70.67 2.6 26.7 66.44 5.0 37.1 62.87 8.8 45.7 60.20 16.4 52.6 58.64 33.3 55.9 58.02 54.9 59.5 58.10 69.9 63.3 58.47 78.2 66.5 59.90 89.8 76.0 62.71 97.3 90.7

Vapor-liquid Equilibrium for Benzene/Acetone[5] P = 101.325 kPa BP Temp. °C % by mole benzene liquid vapor 57.34 11.7 7.4 57.48 12.8 8.1 57.75 15.1 9.5 59.21 26.7 16.6 59.24 27.0 16.7 60.01 32.7 20.2 60.71 37.3 23.1 61.05 39.8 24.7 61.91 45.0 27.9 62.82 50.2 31.7 63.39 53.4 33.9 63.79 55.4 35.3 64.22 57.2 37.0 64.99 61.3 39.9 67.88 73.0 51.2 70.21 80.7 60.1 72.23 86.1 67.9

Vapor-liquid Equilibrium for Benzene/n-Hexane[5] P = 760 mmHg BP Temp. °C % by mole hexane liquid vapor 77.6 7.3 14.0 75.1 17.2 26.8 73.4 26.8 37.6 72.0 37.2 46.0 70.9 46.2 54.0 70.0 58.5 64.4 69.4 69.2 72.5 69.1 79.2 80.7 69.0 82.8 83.8 68.9 88.3 88.8 68.8 94.7 95.0 68.8 96.2 96.4

Spectral data[edit]

UV-Vis
Ionization potential	9.24 eV (74525.6 cm−1)
S1	4.75 eV (38311.3 cm−1)
S2	6.05 eV (48796.5 cm−1)
λmax	255 nm
Extinction coefficient, ε	?
IR
Major absorption bands[6]	(liquid film) Wave number transmittance 3091 cm−1 42% 3072 cm−1 49% 3036 cm−1 27% 1961 cm−1 77% 1815 cm−1 70% 1526 cm−1 81% 1479 cm−1 20% 1393 cm−1 84% 1176 cm−1 86% 1038 cm−1 49% 674 cm−1 4%
NMR
Proton NMR	(CDCl3, 300 MHz) δ 7.34 (s, 6H)
Carbon-13 NMR	(CDCl3, 25 MHz) δ 128.4
Other NMR data
MS
Masses of main fragments

Safety data[edit]

Material Safety Data Sheet for benzene:

Common synonyms	None
Physical properties	Form: colorless liquid
Stability: Stable, but very flammable
Melting point: 5.5 C
Water solubility: negligible
Specific gravity: 0.87
Principal hazards	*** Benzene is a carcinogen (cancer-causing agent).
*** Very flammable. The pure material, and any solutions containing it, constitute a fire risk.
Safe handling	Benzene should NOT be used at all unless no safer alternatives are available.
If benzene must be used in an experiment, it should be handled at all stages in a fume cupboard.
Wear safety glasses and use protective gloves.
Emergency	Eye contact: Immediately flush the eye with plenty of water. Continue for at least ten minutes
and call for immediate medical help.
Skin contact: Wash off with soap and water. Remove any contaminated clothing. If the skin
reddens or appears damaged, call for medical aid.
If swallowed: Call for immediate medical help.
Disposal	It is dangerous to try to dispose of benzene by washing it down a sink, since it is toxic, will cause environmental damage
and presents a fire risk. It is probable that trying to dispose of benzene in this way will also break local
environmental rules. Instead, retain in a safe place in the laboratory (well away from any source of ignition)
for disposal with other flammable, non-chlorinated solvents.
Protective equipment	Safety glasses. If gloves are worn, PVA, butyl rubber and viton are suitable materials.

References[edit]

1. ^Brown; LeMay; Bursten (2006). Chemistry: The Central Science. Upper Saddle River, NJ: Pearson Education. pp. 1067. ISBN0-13-109686-9.
2. ^ ^abcd'Pure Component Properties'(Queriable database). Chemical Engineering Research Information Center. Retrieved 12 May 2007.
3. ^'ETP Entropy of Benzene'(Queriable database). Dortmund Data Bank. Retrieved 7 October 2011.
4. ^Lange's Handbook of Chemistry 10th ed, pp 1522-1524
5. ^ ^abcd'Binary Vapor-Liquid Equilibrium Data'(Queriable database). Chemical Engineering Research Information Center. Retrieved 12 May 2007.
6. ^'Spectral Database for Organic Compounds'. Advanced Industrial Science and Technology. Archived from the original(Queriable database) on 5 May 2006. Retrieved 10 June 2007.

Except where noted otherwise, data relate to standard ambient temperature and pressure.

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