Chapter 7 Thermochemistry Flashcards
What constitutes a system?
A system is the matter that is being observed.
Examples: the total amount of reactants and products in a chemical reaction; the amount of solute and solvent used to create a solution; gas inside a balloon
What constitutes surroundings/the environment?
The surroundings (environment) are everything outside of that system
Explain an isolated system.
Isolated system: the system cannot exchange energy (heat and work) or matter with the surroundings.
Example: an insulated bomb calorimeter
Explain a closed system.
Closed: the system can exchange energy (heat and work) but not matter with the surroundings.
Example: a steam radiator
Explain an open system.
Open: the system can exchange both energy (heat and work) and matter with the surroundings
Example: a boiling pot of water
What does the first law of thermodynamics state?
the change in total internal energy (ΔU) of a system is equal to the amount of heat (Q) transferred to the system minus the amount of work (W) done by the system.
ΔU = Q - W
where:
ΔU is the change in internal energy of the system
Q is the heat added to the system
W is the work done by the system
energy cannot be created, nor destroyed
Explain an isothermal process.
An isothermal process occurs when the system’s temperature is constant. Constant temperature implies the total internal energy of the system (Q) is constant throughout the process, thus ΔU=0, and Q=W (the heat added to the system equals the work done by the system).
Explain an adiabatic process.
An adiabatic process occurs when no heat is exchanged between the system and the environment, thus, the thermal energy of the system is constant throughout the process. When Q=0, the first law of thermodynamics simplifies to ΔQ= -W (the change in internal energy of the system is equal to work done on* the system [the opposite of work done *by the system]).
Explain an isobaric process.
Isobaric processes occur when the pressure of the system is constant. Isobaric process do not alter the first law of thermodynamics.
Explain an isovolumetric (isochoric) process.
Isovolumetric (isochoric) processes experience no change in volume. Because the gas neither expands nor compresses, no work is performed in such a process. W=0. thus the first law of thermodynamics simplifies to: ΔU=Q (the change in internal energy is equal to the heat added to the system).
What do state functions do?
State functions describe the system in an equilibrium state; they cannot describe the process of the system.
State functions: pressure, density, temperature, volume, enthalpy (H), internal energy (U), Gibbs free energy, and entropy (S).
Mnemonic: When I’m under pressure and feeling dense, all I want to do is watch TV and get HUGS.
What are process functions?
Process functions quantitatively describe the pathway taken from one equilibrium state to another.
Examples: work (W) and heat (Q).
What are standard conditions? When are they used?
25C (298K)
1 atm pressure
1M concentrations
used for kinetics, equilibrium, and thermodynamic probles
what are standard temperature and pressure (STP)? When is it used?
0C (273K)
1 atm
used for ideal gas calculations
What is the standard state of a substance?
Under standard conditions, the most stable form of a substance is called the standard state of that substance.
