All Flashcards
What is the effect of adding energy to a solid at its melting point?
The solid will begin to melt, transitioning to the liquid phase, without a change in temperature until all of the solid has melted.
What is the effect of increasing the temperature of a liquid at its boiling point?
The liquid will begin to vaporize, transitioning to the gas phase, without a change in temperature until all of the liquid has vaporized.
What is the effect of increasing pressure on a substance near its melting point?
For most substances, increasing pressure increases the melting point. However, water is an exception; increasing pressure decreases its melting point.
What is the effect of increasing temperature on the volume of a gas (at constant pressure)?
The volume of the gas increases (Charles's Law).
What is the effect of strong intermolecular forces on the heat of vaporization?
Stronger intermolecular forces lead to a higher heat of vaporization because more energy is required to overcome these forces and change the substance from a liquid to a gas.
Define 'heat of fusion' (H).
The energy required for a substance to change from a solid to a liquid.
Define 'heat of vaporization' (Hₜ).
The energy required for a substance to change from a liquid to a gas.
Define 'triple point' on a phase diagram.
The temperature and pressure at which solid, liquid, and gas phases coexist in equilibrium.
Define 'critical point' on a phase diagram.
The point beyond which a distinct liquid phase no longer exists; the substance becomes a supercritical fluid.
Define 'specific heat capacity'.
The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.
Define 'endothermic process'.
A process that absorbs heat from its surroundings.
Define 'exothermic process'.
A process that releases heat to its surroundings.
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.