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ChemistryClass 113 marksmedium
States of Matter
A gas occupies 300 mL at 27 deg C. What volume will it occupy at 127 deg C if the pressure is kept constant?
Reveal model answer + marking pointsHide answer▾
Convert temperatures to Kelvin: T1 = 27 + 273 = 300 K, T2 = 127 + 273 = 400 K. By Charles's law V1/T1 = V2/T2, so V2 = V1 x T2/T1 = 300 x 400/300 = 400 mL.
V1/T1 = V2/T2
Marking-scheme points
- ✓Convert to Kelvin: 300 K and 400 K
- ✓V1/T1 = V2/T2 at constant pressure
- ✓V2 = 300 x 400/300 = 400 mL
ChemistryClass 112 markseasy
States of Matter
Write the ideal gas equation and give the value of the gas constant R in two units.
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The ideal gas equation is PV = nRT, where P = pressure, V = volume, n = number of moles, T = absolute temperature and R = universal gas constant. R = 0.0821 L atm K^-1 mol^-1 = 8.314 J K^-1 mol^-1.
PV = nRT
Marking-scheme points
- ✓PV = nRT
- ✓R = 0.0821 L atm K^-1 mol^-1
- ✓R = 8.314 J K^-1 mol^-1
ChemistryClass 113 marksmedium
States of Matter
Calculate the volume occupied by 2 moles of an ideal gas at 300 K and a pressure of 2 atm. (R = 0.0821 L atm K^-1 mol^-1)
Reveal model answer + marking pointsHide answer▾
Using PV = nRT, V = nRT/P = (2 x 0.0821 x 300) / 2 = 49.26/2 = 24.63 L.
V = nRT / P
Marking-scheme points
- ✓Use V = nRT/P
- ✓Substitute n=2, R=0.0821, T=300, P=2
- ✓V = 24.63 L
ChemistryClass 113 marksmedium
States of Matter
State the main postulates of the kinetic molecular theory of gases.
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States of Matter
Write the van der Waals equation for n moles of a real gas and explain the significance of the constants a and b.
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Thermodynamics
Define system and surroundings. Name the three types of thermodynamic systems.
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Thermodynamics
State the first law of thermodynamics and give its mathematical expression with sign convention.
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Thermodynamics
When 1 kJ of heat is supplied to a gas, it does 200 J of work by expanding. Calculate the change in internal energy of the gas.
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Thermodynamics
Define enthalpy. Derive the relation between delta H and delta U for a reaction involving gases.
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Thermodynamics
Given: C(s) + O2(g) -> CO2(g), delta H = -393.5 kJ and CO(g) + 1/2 O2(g) -> CO2(g), delta H = -283.0 kJ. Calculate the enthalpy of formation of CO(g).
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Thermodynamics
State Hess's law of constant heat summation and mention one of its applications.
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Thermodynamics
What is entropy? Predict the sign of delta S when ice melts into water.
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Thermodynamics
Write the Gibbs-Helmholtz equation and state the criteria of spontaneity in terms of delta G.
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Thermodynamics
For a reaction, delta H = -92.4 kJ and delta S = -198 J/K at 298 K. Calculate delta G and predict whether the reaction is spontaneous.
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Thermodynamics
Define standard enthalpy of formation and standard enthalpy of combustion.
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Equilibrium
What is a reversible reaction? State two characteristics of chemical equilibrium.
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Equilibrium
For the reaction N2(g) + 3H2(g) <=> 2NH3(g), write the expression for Kc and state the relation between Kp and Kc.
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Equilibrium
For the equilibrium N2O4(g) <=> 2NO2(g), the equilibrium concentrations are [N2O4] = 0.02 mol/L and [NO2] = 0.04 mol/L. Calculate Kc.
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Equilibrium
State Le Chatelier's principle. What is the effect of increasing pressure on the equilibrium N2(g) + 3H2(g) <=> 2NH3(g)?
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Equilibrium
What is the effect of temperature and of a catalyst on a system at equilibrium?
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