Chemistry Concepts: Heat, Gas Laws, Dilution

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.