Questions and Answers
- A cylinder of volume 1810 dm3 contains gas at a pressure of 197 atm and temperature of 25°C. Assuming that the gas behaves as a perfect gas, calculate the amount of gas contained in the cylinder.
- A pressure vessel contains a gaseous mixture made up of 2.34 kg silane, SiH4, and 55.4 kg argon, Ar. Determine the mole fraction of silane.
- The partial pressure of ethanol in the air above a sample of liquid ethanol is 1400 Pa. Assuming the air to be at normal pressure, calculate the mole fraction of ethanol in the air.
- Calculate the work done on the system when 1.00 mol of gas held behind a piston expands irreversibly from a volume of 1.00 dm3 to a volume of 10.0 dm3 against an external pressure of 1.00 bar.
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- 1.00 mol of gas in a cylinder is compressed reversibly by increasing the pressure from 1.00 bar to 10.0 bar at a constant temperature of 500 K. Calculate the work done on the gas by the compression.
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- The temperature of a copper block of mass 423 g rises by 10.1 °C. Calculate the heat transferred, given that the specific heat capacity of copper is 385 J K–1 kg–1.
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- Raising the temperature of 1.00 dm3 of water from a temperature of 25°C to 100°C at constant pressure requires 312 kJ of heat. Calculate the molar heat capacity of water at constant pressure.
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- A calorimeter was calibrated by passing an electrical current through a heater and measuring the rise in temperature that resulted. When a current of 113 mA from a 24.1 V source was passed through the heater for 254 s, the temperature of the calorimeter rose by 2.61 °C. Determine the heat capacity of the calorimeter.
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- A perfect gas expands reversibly at a constant temperature of 298 K so that its volume doubles. What is the change in the molar internal energy of the gas?
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- Which of the following statements is always true for a reaction in which there is no non- expansion work?
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- Calculate the difference between the molar internal energy and the molar enthalpy for a perfect gas at 298.15 K.
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- For many substances, the variation with temperature of the molar heat capacity at constant pressure of is given by the expression For copper, a = 22.64 J K–1 mol–1, b = 6.28 ´ 10–3 J K–2 mol–1 with the value of c being negligible. Calculate the change in the molar enthalpy of copper when it is heated from 293 to 323 K.
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- The molar heat capacity at constant volume of argon, Ar, is 12.47 J K mol–1. What is the value of the molar heat capacity at constant pressure?
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In an experiment to determine its enthalpy of vaporization, liquid tetrachloromethane, CCl4, was placed in an open boiler that was equipped with a resistive heating coil and brought to the boil at a constant temperature of 350 K and pressure of 1 bar. The passage of a current of 0.933 A from a 24.0 V supply for 30.0 s was found to result in the vaporization of 3.45 g of tetrachloromethane. Calculate the standard enthalpy of vaporization of tetrachloromethane at 350 K.
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- For iodine, I2, at 114°C, the standard enthalpy of fusion is 16.1 kJ mol–1 and the standard enthalpy of vaporization is 45.0 kJ mol–1. Calculate the standard enthalpy of sublimation at this temperature.
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- The energy released as heat when liquid propanone, CH3COCH3, is burned in a bomb calorimeter at 298.15 K is 1788 kJ mol–1. Calculate the enthalpy of combustion of propanone.
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- Estimate the standard enthalpy change for the processF2(g) + 2 e–(g) ® 2 F–(g) The F–F bond enthalpy is +155 kJ mol–1 and the electron gain enthalpy of elemental fluorine, F, is –
328 kJ mol–1.
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- Use the following data to calculate the mean B–Cl bond enthalpy in boron trichloride, BCl3.DHʅ(298 K) Enthalpy of atomization of boronB(s) ® B(g) +590 kJ mol–1Enthalpy of atomization of chlorineCl2(g) ® 2 Cl(g) +242 kJ mol–1Enthalpy of formation of boron trichlorideB(s) + 3/2 Cl2(g) ® BCl3(g) –418 kJ mol–1
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- Calculate the standard enthalpy of combustion of phenol, C6H5OH, at 298.15 K given that, at this temperature, the standard enthalpy of formation of phenol is –165.0 kJ mol–1, of liquid
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estimate the standard enthalpy of formation of liquid benzene, C6H6, at 298.15 K. At this temperature, the standard enthalpy of atomization of carbon C(s, graphite) ® C(g) is +717 kJ mol–1 and the standard enthalpy of vaporization of benzene is 34 kJ mol–1, whilst the standard bond enthalpy of hydrogen, H2, is 436 kJ mol–1. The mean bond enthalpy of a C6H5–H bond is 469 kJ mol–1 and of an aromatic C–C bond is 452 kJ mol–1.
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- Calculate the standard enthalpy change for the hydrogenation reactionC2H4(g) + H2(g) ® C2H6(g) at 298.15 K. At this temperature, the standard enthalpy of combustion of ethene, C2H4, is –1409 kJ mol–1, of hydrogen, H2, is –286 kJ mol–1 and of ethane, C2H6 is –1560 kJ mol–1.
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- The standard enthalpy of combustion of propane, C3H8, is –2.220 ´ 103 kJ mol–1 at 400 K. Use the data below, and Kirchhoff's law, to calculate the standard enthalpy of combustion at 600 K. Cʅp,m / J K–1 mol–1C3H8(g) 73.6O2(g) 29.4H2O(g) 33.6CO2(g) 37.1
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Study Notes
Gas Properties and Calculations
- Volume of a cylinder containing gas: 1810 dm³
- Pressure of gas: 197 atm
- Temperature: 25°C
- Ideal gas behavior considered for calculations of gas amount.
Mixture Calculations
- Gaseous mixture consists of silane (SiH₄) and argon (Ar).
- Mass of silane: 2.34 kg
- Mass of argon: 55.4 kg
- Found mole fraction of silane to determine its proportion in the mixture.
Partial Pressure and Mole Fraction
- Partial pressure of ethanol is 1400 Pa.
- Normal atmospheric pressure needed to calculate ethanol's mole fraction in the air.
Work Done on Gas
- Irreversible expansion of 1.00 mol of gas from 1.00 dm³ to 10.0 dm³ against 1.00 bar external pressure calculates work done on the system.
- Reversible compression of 1.00 mol gas in a cylinder from a pressure of 1.00 bar to 10.0 bar at 500 K also involves work done calculation.
Heat Transfer and Capacity
- Mass of copper block: 423 g; temperature rise: 10.1°C; specific heat capacity: 385 J K⁻¹ kg⁻¹ used for heat transfer calculation.
- Heat required to raise 1.00 dm³ of water from 25°C to 100°C: 312 kJ, allows for calculation of molar heat capacity at constant pressure.
- Calorimeter heat capacity determined through electrical current measurements affecting temperature rise.
Thermodynamic Properties of Gases
- Perfect gas expands reversibly at 298 K, volume doubles, leading to no change in molar internal energy.
- Difference between molar internal energy and molar enthalpy for a perfect gas at 298.15 K identified.
Heat Capacity and Change
- Variation of molar heat capacity at constant pressure is described with specific parameters for copper, allowing for change in molar enthalpy calculation when heated from 293 K to 323 K.
- Molar heat capacity at constant volume of argon is given as 12.47 J K mol⁻¹ with a conversion to constant pressure capacity.
Enthalpy Calculations
- Standard enthalpy of vaporization for tetrachloromethane (CCl₄) derived from electrical heating methods.
- Standard enthalpy of fusion for iodine (I₂) and vaporization provide basis for calculating sublimation enthalpy.
- Enthalpy of combustion for liquid propanone (CH₃COCH₃) calculated from energy released in combustion reaction.
Reaction Energetics
- Standard enthalpy changes from reaction data, like F₂ and electron interactions, involve bond enthalpies and electron gain enthalpies.
- Mean B–Cl bond enthalpy in boron trichloride (BCl₃) determined using electronegativity data.
- Standard enthalpy of combustion for phenol (C₆H₅OH) determined alongside formation enthalpy of benzene (C₆H₆) considering various energy measures.
- Hydrogenation reaction enthalpy change calculation based on standard combustion enthalpies provided.
Temperature Effects on Enthalpy
- Standard enthalpy of combustion of propane (C₃H₈) assessed at different temperatures using Kirchhoff's law and specific heat capacities data for changes in conditions.
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Description
Calculate the amount of gas in a cylinder using the ideal gas law, given volume, pressure, and temperature. Practice problem for chemistry and physics students.
