Ch. 7: Thermochemistry Flashcards
What is the difference between an isolated, closed, and open system?
Isolated: cannot exchange energy (heat, work) or matter with surroundings
Closed: can exchange energy (heat, work) but cannot exchanged matter
Open: can exchange energy (heat, work) AND matter
What is the first law of thermodynamics?
The change in internal energy of a system will be equal to the energy added as heat minus the work done BY the system.
∆U = Q - W
How do isothermal processes affect the total internal energy of a system?
Isothermal: constant temperature
Constant temperature implies that the ∆U of the system is constant throughout the process. Therefore Q = W (the heat added to the system is equal to the work done by the system)
What does isothermal expansion look like on a P-V graph?
Appears hyperbolic. The area under the curve is equal to work done by the system (which is also equal to the heat that entered the system because Q = W)
What is an adiabatic process and how does it affect the total internal energy of a system?
Adiabatic: no heat exchange, Q = 0
Since thermal energy is constant, ∆U = -W meaning that the total internal energy is equal to the work done ON the system by the surroundings (as apposed to the work done by the system on the surroundings)
What does adiabatic expansion look like on a P-V graph?
Appear hyperbolic. Temperature changes but there is no heat exchange. The area under the curve is equal to work.
How do isobaric processes affect the total internal energy of the system?
Isobaric: constant pressure
This does NOT alter the first law of thermodynamics.
What does isobaric expansion look like on a P-V graph?
Appears as a flat line. Slope is zero and the area under the curve equals work.
How do isovolumetric processes affect the total internal energy of the system?
Isovolumetric: constant volume
Since volume does not change, there is no work done by or on the system. Thus, ∆U = Q (the change in internal energy is equal to the heat added).
What does isovolumetric expansion look like on a P-V graph?
Vertical line, no slope, and there is no area under the curve
What is the difference between a state and process function?
State functions are independent of the path taken to reach equilibrium. They cannot describe how a system got to its current equilibrium.
Process functions are dependent on the pathway taken from one equilibrium state to another (heat, work).
List the 8 state functions?
Pressure Density Temperature Volume Enthalpy Internal Energy Gibbs Free Energy Entropy
When I’m under PRESSURE and feeling DENSE, all I want to do is watch TV and get HUGS
What is the difference between standard conditions and STP?
Standard conditions are used to for kinetics, equilibrium, and thermodynamics problems = 298K, 25°C, 1 atm, 1 M concentrations
STP is standard temperature and pressure used for gas law calculations = 273 K, 0°C, 1 atm
What is the difference between ∆H°, ∆S°, ∆G° and ∆H, ∆S, ∆G?
∆H°, ∆S°, ∆G° represent changes in enthalpy, entropy, and Gibb’s free energy under standard conditions (298K, 25°C, 1 atm, 1 M)
∆H, ∆S, ∆G are not under standard conditions
What is vaporization? How does it affect temperature? Is the process endothermic or exothermic and why?
Vaporization is when high kinetic energy molecules move from the liquid to gas phase. As more molecules move to the gas phase, the temperature of the liquid decreases. This process is endothermic because the liquid needs energy input from the surroundings (such as the sun) to turn into gas.
How is boiling different than vaporization?
Boiling is a specific type of vaporization that occurs only under certain conditions. Boiling only occurs above the BP of a liquid.
Define boiling point in terms of vapor pressure.
The boiling point of a liquid is when the vapor pressure above the liquid equals the ambient pressure (external pressure)
How does temperature affect vapor pressure?
Vapor pressure INCREASES as temperature INCREASES because more molecules have sufficient kinetic energy to escape to the gas phase.
What is condensation? What conditions facilitate condensation?
Condensation is when gas molecules move into the liquid phase. The process is facilitated by lower temperature or higher pressure.
Describe what happens to the molecules in a solid and their energy as temperature increases.
As temperature increases, molecules have greater freedom of movement and energy disperses (increase in number of microstates). If there is enough energy then atoms or molecules will escape into the liquid phase.
What is sublimation? Example?
Solid to gas
Example: Dry ice (solid CO2)
