Ch 3 - Thermodynamics Flashcards
What is the zeroth law of thermodynamics?
states that objects are in thermal equilibrium when they are at the same temperature
- if a=b and b=c, then a=c
What do objects in thermal equilibrium experience?
no net exchange of heat energy
What is temperature?
- a qualitative measure of how hot or cold an object is
- quantitatively, it is related to the average kinetic energy of the particles that make up a substance
What is thermal expansion?
describes how a substance changes in length or volume as a function of the change in temperature
What is the difference between a system and the surrounding?
- a thermodynamic system is the portion of the universe that we are interested in observing
- the surroundings include everything that is not part of the system
What are the 3 types of systems?
- isolated: do not exchange matter or energy with the surroundings
- closed: exchange energy but not matter with their surroundings
- open: exchange both energy and matter with their surroundings
What are state functions?
- pathway independent and are not themselves defined by a process
- pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy
What are process functions?
- describe the pathway from one equilibrium state to another
- work and heat
What is the first law of thermodynamics?
- a statement of conservation of energy: the total energy in the universe can never decrease or increase
- an increase in U is caused by transferred heat into the system or performing work on the system
- U will decrease when heat is lost from the system or work is performed by the system
What is the total internal energy of a closed system equal to?
the heat flow into the system minus the work done by the system
delta U = Q - W
What is heat?
- the process of energy transfer between 2 objects at different temperatures that occurs until the 2 objects cone into thermal equilibrium (reach the same temperature)
What is specific heat?
- the amount of energy necessary to raise one gram of a substance by one degree Celsius or one Kelvin
- specific heat of water is 1 cal/g.K
What is the heat of transformation?
- during a phase change, heat energy causes changes in the particles’ potential energy and energy distribution (entropy), but no kinetic energy
- therefore, there is no change in temperature
What are the 4 special types of thermodynamic systems in which a given variable is held constant?
- isothermal: the temperature is constant, and the change in internal energy is 0
- adiabatic: no heat exchanged
- isobaric: the pressure is constant
- isovolumetric (isochoric): the volume is constant and the work done by or on the system is 0
What is the second law of thermodynamics?
states that in a closed system (up to and including the entire universe), energy will spontaneously and irreversibly go from being localized to being spread out (dispersed)
What is entropy?
a measure of how much energy has spread out and how spread out energy has become
How do microstates relate to entropy?
on a statistical level, as the number of microstates increases, the potential energy of a molecule is distributed over that larger number of microstates, increasing entropy
Are natural processes irreversible or reversible?
- every natural process is ultimately irreversible
- under highly controlled conditions, certain equilibrium process such as phase changes can be treated as essentially reversible
How do you convert between temperature units?
F = 9/5.C + 32 K = C + 273
What is the coefficient of linear expansion?
deltaL = alpha.L.deltaT
constant (alpha) that characterizes how a specific material’s length changes as the temperature changes
What is the coefficient of volumetric expansion?
deltaV = beta.V.deltaT
a constant that characterizes how specific material’s volume changes as the temperature changes
What is the maximum distance that 2 object can be from one another and still adhere to the zeroth law of thermodynamics?
- there is no set distance
- as long as the 2 objects are in thermal contact and at the same temperature, they are in thermal equilibrium
What does a negative or positive change in internal energy mean?
- neg: decreasing temperature
- pos: increasing temperature
What does a negative or positive heat mean?
- neg: heat flows out of the system
- pos: heat flows into the system
What does a negative or positive work mean?
- neg: work is done on the system (compression)
- pos: work is done by the system (expansion)
How much heat is required to raise 1 g of water by 1 C?
- 1 calorie (cal)
- 1 Calorie needed to raise 1 kg of water by 1C
1 Cal = 1000 cal = 4184 J
What is conduction?
the direct transfer of energy from one molecule to another through molecular collisions
What is convection?
the transfer of heat by the physical motion of a fluid over a material
What is radiation?
the transfer of energy by electromagnetic waves
What equation relates heat gained or lost by an object and the changes in temperature of that object?
q = mcdeltaT
How do you calculate heat energy of a phase change?
q= mL
L is the heat of transformation (latent heat)
What are the terms for the following:
- solid to liquid
- liquid to solid
- liquid to gas
- gas to liquid
- solid to gas
- gas to solid
- s>l = fusion or melting
- l>s = freezing or solidification
- l>g = boiling, evaporation, or vaporization
- g>l = condensation
- s>g = sublimation
- g>s = deposition
How is entropy calculated?
deltaS = Qrev/T –> J/mol.K
What is the relationship between entropy of a system and its surroundings for any given thermodynamic process?
- Suniverse = Ssystem + Ssurroundings > 0
- entropy of the isolated system and surroundings will never decrease; either remain 0 or increase
- entropy of a system can decrease as long as the entropy of its surroundings increased by at least as much
