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Compare and contrast heating curves and cooling curves.
Heating curves: Endothermic, temperature increases with energy added, shows melting and vaporization. Cooling curves: Exothermic, temperature decreases with energy released, shows condensation and freezing. Both: Have slopes (temperature change) and plateaus (phase change).
Compare heat of fusion (H) and heat of vaporization (Hₜ).
H: Energy to change solid to liquid. Hₜ: Energy to change liquid to gas. Hₜ is almost always greater than H because all IMFs must be broken to vaporize.
Compare the processes occurring during the slopes versus the plateaus of a heating curve.
Slopes: Temperature changes, kinetic energy increases, q = mcΔT. Plateaus: Phase changes, potential energy increases (breaking IMFs), temperature remains constant, q = H(m) or Hₜ(m).
Differentiate between heat of vaporization and heat of condensation.
Heat of Vaporization: Energy absorbed when a liquid changes to a gas (endothermic). Heat of Condensation: Energy released when a gas changes to a liquid (exothermic); it's the negative of the heat of vaporization.
Differentiate between heat of fusion and heat of freezing.
Heat of Fusion: Energy absorbed when a solid changes to a liquid (endothermic). Heat of Freezing: Energy released when a liquid changes to a solid (exothermic); it's the negative of the heat of fusion.
On a typical heating curve, what do the slopes represent?
The slopes represent the change in temperature as heat is added within a single phase (solid, liquid, or gas).
On a typical heating curve, what do the plateaus represent?
The plateaus represent phase changes (melting/freezing, boiling/condensation) where the temperature remains constant as heat is added or removed.
On a phase diagram, what area represents the solid phase?
The solid phase is generally located in the high pressure and low temperature region of the phase diagram.
On a phase diagram, what area represents the liquid phase?
The liquid phase is generally located in the moderate pressure and moderate temperature region of the phase diagram.
On a phase diagram, what area represents the gas phase?
The gas phase is generally located in the low pressure and high temperature region of the phase diagram.
What are the steps to calculate the energy needed to convert ice at -20°C to steam at 140°C?
1: Heat ice from -20°C to 0°C using q = mcΔT. 2: Melt ice at 0°C using q = H(m). 3: Heat water from 0°C to 100°C using q = mcΔT. 4: Vaporize water at 100°C using q = Hₜ(m). 5: Heat steam from 100°C to 140°C using q = mcΔT. 6: Sum all the q values.
Describe the process represented by the plateaus on a heating curve.
During plateaus, energy is used to overcome intermolecular forces and change the phase of the substance (melting or vaporization), without changing the temperature.
Outline the steps to determine the volume of air needed for complete combustion of a given mass of propane.
1: Calculate moles of propane. 2: Use stoichiometry to find moles of O₂ needed. 3: Use the ideal gas law (PV=nRT) to find the volume of O₂. 4: Divide the volume of O₂ by the percentage of O₂ in air (21%) to find the volume of air.
What steps are involved in calculating the heat of formation (ΔH°) of a compound using heats of combustion?
1: Write the balanced chemical equation for the combustion reaction. 2: Use the formula: ΔHₑₘₒ = ΣnΔH°(products) - ΣnΔH°(reactants). 3: Plug in known values for ΔHₑₘₒ and ΔH° of products and reactants. 4: Solve for the unknown ΔH°.
Describe the process of energy change during cooling curves.
Energy is released as a substance cools; heat of condensation equals -Hₜ, heat of freezing equals -H.