Gas Law Review

​CHM 111 Test 5 Review

​Units 9-10

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​Topic 9: Gases

Major Content:

• Kinetic Molecular Theory

• Gas Law Formulas

• Real vs. Ideal Gases

• Gas Stoichiometry

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​Kinetic Molecular Theory

Assumptions:

1. Gas molecules move in random lines and maintain their speed even during collisions

2. ​Gas motion is determined by

   1. temperature of molecules

   2. molar mass of molecules ​

Multiple Choice

As the temperature of a substance increases:

• The speed, and average kinetic energy of the particles, both increase.

• The speed, and average kinetic energy of the particles, both decrease.

• The speed of the particles increases, but the average kinetic energy of the particles decreases.

• The speed of the particles decreases, but the average kinetic energy of the particles increases.

​Gas Laws

Gas Variables

• pressure

• volume

• temperature

• moles

• ideal gas constant, R​

​

Gas Laws

• Boyle's Law

• Charles' Law

• Gay-Lussac's Law

• Combined Gas Law

• Ideal Gas Law​

​

Multiple Choice

A gas sample is held at constant pressure. The gas occupies 3.62 L of volume when the temperature is 21.6°C. Determine the temperature at which the volume of the gas is 3.42 L.

• 312K

• 278K

• 20.4K

• 295K

• 552K

​Real vs. Ideal Gases

No gas actually behaves 'ideally'

• deviates from ideal behavior at high pressures and low temperatures

• due to interaction of molecules and how much space they occupy​

Multiple Choice

Calculate the volume that a 0.323-mol sample of a gas will occupy at 265 K and a pressure of 0.900 atm.

• 7.18 L 

• 7.80 L

• 4.63 L

• 4.36 L

​Gas Stoichiometric Calculations

Multiple Choice

Mg₃N₂ + 3H₂O → 3MgO + 2NH₃

If 10.3 g of magnesium nitride is used, what volume of ammonia gas would be collected at 20.0°C and 0.989 atm?

• 14.5 L NH₃

• 4.96 L NH₃

• 0.261 L NH₃

• 24.9 L NH₃

​Topic 10: Thermochemical Equations

Major Content:

• ​Thermochemical equations and stoichiometry

• Calculating Enthal​py

  • Hess's Law

  • Standard Enthalpy of Formation

  • Bond Energies

  • Calorimetry

​Thermochemical Equations

Multiple Choice

What mass of P₄ must be reacted to produce 5905 kJ of energy?
P₄ + 6Cl₂ --> 4PCl₃ + 2439 kJ

• 25.43 g

• 563.0 g

• 2.421 g

• 300.0 g

​Determining Enthalpy: Hess's Law

Manipulating given reactions (and their enthalpies) so that when the combine, the form a desired reaction​

Multiple Choice

Consider the following equations.

Mg(s) + O₂(g) → MgO(s) ∆H = –602 kJ

H₂(g) + O₂(g) → H₂O(g) ∆H = –242 kJ

What is the ∆H value (in kJ) for the following reaction?

MgO(s) + H₂(g₎ → Mg(s) + H₂O(g)

• -844

• -360

• +360

• +844

​Determining Enthalpy: Formation Values

​1. Multiply the given ΔH_f values of each reactant and product by how many appear in the given reaction

2. Sum the total values of enthalpy on the reactant and products side

3. Δ​H_rxn is found by subtracting the product total - reactant total

Multiple Choice

Calculate the enthalpy of reaction (ΔH).

4CO_{2 (g)} + 6H₂O _(g) → 2C₂H_{6 (g)} + 7O_{2 (g)}

ΔH_f^o [CO_2(g)] = -393.5 kJ

ΔH_f^o [H₂O_(g)] = -241.8 kJ

ΔH_f^o [C₂H_6(g)] = -84.7 kJ

ΔH_f^o [O_2(g)] = 0 kJ

• 550.647 KJ/mol

• 2855.584 KJ/mol

• -550.647 KJ/mol

• -2855.584 KJ/mol

Enthalpy using Bond Energies

Energy of bonds broken - energy of bonds formed

Multiple Choice

Using the table of average bond energies below the image, the ΔH for the reaction in kJ is.....

• + 160 kJ
• -63 kJ
• - 160 kJ
• -217 kJ

Calorimetry

Fill in the Blanks

A sample of iron receives 50.J of heat energy that raises the temperature of the iron by 25.0°C. If iron has a specific heat of 0.10 J/g°C, what is the mass of the iron sample?

grams

Multiple Choice

15.0 gram sample of a metal at 200C is added to 100 grams of water (S= 4.184) at 25C. The ending temperature of both species is 28C.

What is the specific heat of the metal?

• 1.255

• 0.836

• 0.489

• 0.211