Chemistry Concepts: Heat, Gas Laws, Dilution

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Questions and Answers

Which of the following is the correct Lewis structure for the selenium difluoride molecule (SeF2)?

  • F Se F
  • F Se F (correct)
  • F Se F (correct)
  • F Se F (correct)

What is the correct ranking of the bonds in order of increasing polarity: N-H, Br-O, C-Cl?

  • C-Cl < N-H < Br-O
  • Br-O < C-Cl < N-H
  • N-H < C-Cl < Br-O
  • Br-O < N-H < C-Cl (correct)

What is the AXE classification for the SF2 molecule?

  • AX3E1
  • AX2E1 (correct)
  • AX2E2
  • AX3E0

What is the electron geometry around the central atom in the NO2- ion?

<p>trigonal planar (C)</p> Signup and view all the answers

How many questions are included in this exam?

<p>34 (C)</p> Signup and view all the answers

What should you do if a question on the exam appears ambiguous or unclear?

<p>Raise your hand and ask for clarification (A)</p> Signup and view all the answers

What will happen if a student makes a mistake while using a pen on the bubble sheet?

<p>There is no way to correct it (A)</p> Signup and view all the answers

What is the maximum number of points available on this exam before extra credit?

<p>102 points (B)</p> Signup and view all the answers

What is the mass of the graphite sample if 312.5 cal of heat energy raises its temperature from 28.21°C to 76.87°C, given a specific heat of 2.036 cal/g°C?

<p>6.055 g (A)</p> Signup and view all the answers

Which processes are correctly classified as endothermic or exothermic?

<p>Condensation: exothermic, Sublimation: endothermic, Vaporization: exothermic (B)</p> Signup and view all the answers

During which segment of the heating curve is water in the solid state?

<p>Below 0°C (A)</p> Signup and view all the answers

What is the pressure inside a 65.00 L tank containing 200.0 g of oxygen gas at a temperature of 75.00 °C?

<p>1.373 atm (D)</p> Signup and view all the answers

What is the final concentration of a diluted cobalt chloride solution if 11.85 mL of a 6.345 g/L solution is diluted with 19.37 mL of water?

<p>3.882 g/L (B)</p> Signup and view all the answers

Which statement accurately describes the phase of water during the phase change at 0°C?

<p>Water can exist as a solid or liquid. (D)</p> Signup and view all the answers

What occurs during the process of sublimation?

<p>Solid to gas without becoming liquid (A)</p> Signup and view all the answers

In the context of heating water, what happens at the boiling point?

<p>Water changes from liquid to gas. (C)</p> Signup and view all the answers

What is the molecular shape of the NH3 molecule?

<p>trigonal pyramid (C)</p> Signup and view all the answers

What is the molecular geometry of the SO2 molecule?

<p>bent (A)</p> Signup and view all the answers

Which of the following correctly classifies CHF3, PF3, and CCl4 as polar or nonpolar?

<p>polar, polar, nonpolar (D)</p> Signup and view all the answers

Identify the strongest intermolecular force acting in SO3, CH3OCH3, and PCl3.

<p>dipole-dipole forces, hydrogen bonds, London dispersion forces (C)</p> Signup and view all the answers

Arrange the following substances in order of increasing boiling point: CH3OH, CH3F, CH3CH3.

<p>CH3CH3 &lt; CH3OH &lt; CH3F (C)</p> Signup and view all the answers

Which intermolecular force is predominant in CH3OH?

<p>hydrogen bonding (B)</p> Signup and view all the answers

Which molecule listed is nonpolar?

<p>CCl4 (C)</p> Signup and view all the answers

Which molecular shape is associated with a molecule having a lone pair and three bonded pairs?

<p>trigonal pyramidal (C)</p> Signup and view all the answers

What is the mass of 0.6027 mole of potassium sulfate?

<p>197.7 g (C)</p> Signup and view all the answers

What mass of sodium has the same number of atoms as 15.00g of sulfur?

<p>8.837 g (A)</p> Signup and view all the answers

What is the coefficient for O2 (g) when balancing the equation NH3 (g) + O2 (g) → NO (g) + H2O (g)?

<p>2 (A)</p> Signup and view all the answers

Identify the formula of the precipitate formed from lead(II) nitrate and potassium iodide?

<p>PbI2 (C)</p> Signup and view all the answers

What is the maximum mass of nitric acid that can be produced from 52.00g of H2O2?

<p>192.7 g (B)</p> Signup and view all the answers

How many moles of copper(II) sulfate are present in 62.765 g of copper(II) sulfate?

<p>2.543 mol (D)</p> Signup and view all the answers

Which of the following mixtures will produce a precipitate?

<p>Ni(NO3)2 (aq) + Na2CO3 (aq) (D)</p> Signup and view all the answers

What is the boiling point order from lowest to highest for the following alcohols?

<p>A.OH &lt; B.OH &lt; C.OH &lt; D.OH &lt; E.OH (A)</p> Signup and view all the answers

Which reaction will have the fastest rate in the forward direction when A(g) and B(g) are mixed at 0.500 M each?

<p>Reaction B (B)</p> Signup and view all the answers

At equilibrium, which of the following statements must be correct?

<p>The rate of the forward reaction equals the rate of the reverse reaction. (C)</p> Signup and view all the answers

Identify the correct equilibrium expression for this reaction: 4 CH4 (g) + S8 (s) ⇌ 4 CS2 (g) + 8 H2 (g).

<p>$K = \frac{[CS2]^4 [H2]^8}{[CH4]^4}$ (A)</p> Signup and view all the answers

What will happen to the equilibrium when the temperature of the reaction N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g) is raised?

<p>Shifts toward reactants (B)</p> Signup and view all the answers

What effect does adding more N2 have on the equilibrium of the reaction system N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g)?

<p>Shifts toward products (C)</p> Signup and view all the answers

What happens to the reaction system when the volume is decreased?

<p>Shifts toward the side with fewer gas molecules (B)</p> Signup and view all the answers

Which of the following conditions changes the rate of reaction without affecting the equilibrium constant?

<p>Adding a catalyst (D)</p> Signup and view all the answers

Which statement about equilibrium concentrations is true?

<p>Concentrations of reactants and products remain constant (C)</p> Signup and view all the answers

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Study Notes

Specific Heat

  • The specific heat of graphite is 2.036 cal/g°C.
  • When 312.5 cal of heat energy are applied to a sample of graphite, the temperature of the graphite increases from 28.21°C to 76.87°C.
  • The mass of the sample of graphite is 13.08 g.

Endothermic and Exothermic Processes

  • Condensation is an exothermic process.
  • Sublimation is an endothermic process.
  • Vaporization is an endothermic process.

Heating Curve of Water

  • The heating curve of water shows the different phases of water present as heat is added.
  • During the segment of the curve indicated, the phase of water present is liquid only.

Gas Laws

  • 200.0 g of oxygen gas are sealed in a 65.00 L tank at a temperature of 75.00 °C.
  • The pressure inside the tank is 2.747 atm.

Solution Dilution

  • A solution of cobalt chloride has a concentration of 6.345 g/L.
  • 11.85 mL of this solution are diluted by adding 19.37 mL of water.
  • The final concentration of the diluted solution is 3.882 g/L.

Lewis Structures

  • The Lewis structure of selenium difluoride (SeF2) has the following arrangement:
    • F Se F

Molecular Geometry and Polarity

  • The AXE classification for SF2 is AX2E2.
  • The geometry around the central atom in the NO2- ion is bent.
  • The molecular shape of the NH3 molecule is trigonal pyramid.
  • The molecular shape of the SO2 molecule is bent.
  • CHF3 is polar.
  • PF3 is polar.
  • CCl4 is nonpolar.

Intermolecular Forces

  • The strongest intermolecular force operating in SO3 is London dispersion forces.
  • The strongest intermolecular force operating in CH3OCH3 is dipole-dipole forces.
  • The strongest intermolecular force operating in PCl3 is dipole-dipole forces.

Boiling Point

  • The order of increasing boiling point for CH3OH, CH3F, and CH3CH3 is CH3CH3 < CH3F < CH3OH.

Stoichiometry

  • The mass of sodium that has the same number of atoms as 15.00g of sulfur is 8.837 g.
  • 0.6027 mole of potassium sulfate has a mass of 105.0 g.
  • 62.765 g of copper(II) sulfate contains 0.3932 mol.

Balancing Chemical Equations

  • The balanced chemical equation for the reaction of NH3 (g) and O2 (g) to form NO (g) and H2O (g) is:
    • 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g)
  • The coefficient for O2 (g) in the balanced equation is 5.

Limiting Reactants and Stoichiometry

  • The maximum mass of nitric acid that can be prepared from 52.00 g of H2O2 and excess N2H4 in the reaction N2H4 (l) + 7 H2O2 (aq) → 2 HNO3 (aq) + 8 H2O (l) is 96.34 g.

Precipitation Reactions

  • The precipitate formed when aqueous solutions of lead(II) nitrate and potassium iodide are mixed is PbI2.

Reaction Energy Diagrams

  • The reaction energy diagram with the lowest activation energy will have the fastest rate in the forward direction.

Chemical Equilibrium

  • At equilibrium, the rate of the forward reaction and the rate of the reverse reaction are equal.

  • The equilibrium equation associated with the reaction: 4 CH4 (g) + S8 (s) 4 CS2 (g) + 8 H2 (g) is:

    K= [CS2 ]^4 [H2 ]^8 [CH4 ]^4

Le Chatelier's Principle

  • The equilibrium will shift toward products when N2 is added to the reaction system N2 (g) + 3 H2 (g) 2 NH3 (g) ∆H = –22.1 kcal.
  • The equilibrium will shift toward reactants when the temperature is raised for the reaction system N2 (g) + 3 H2 (g) 2 NH3 (g) ∆H = –22.1 kcal.
  • The equilibrium will shift toward products when the volume is decreased for the reaction system N2 (g) + 3 H2 (g) 2 NH3 (g) ∆H = –22.1 kcal.

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