Unit 4: Thermochemistry Flashcards
What is thermochemistry?
It is an area of chemistry concerned with heat affects accompanying chemical reactions, energy, and spontaneity.
What is energy (U)?
The capacity to do work or produce heat.
What is a system?
part of the universe we are studying.
What is surroundings?
Everything else in the universe.
What is work (w)?
Energy transfer due to moving against a force.
What is heat (q)?
Energy transfer due to anything other than work.
What is an open system?
Exchange of heat/work & matter between the system & surroundings.
What is a closed system?
Exchange of heat/work between the system & surroundings.
What is an isolated system?
No exchange of heat/work or matter between system & surroundings.
What is an adiabatic system?
Exchange or work between system & surroundings.
What is a state function?
They are functions or properties of a thermodynamic system. They do not depend on how that condition was reached.
P, V, T, n, and U are state functions.
Are heat and work state functions?
No
What is the first law of thermodynamics?
The total energy of a system remains constant, even if it is converted from one form to another.
What does internal energy (U) consist of?
- Transitional energy (motion)
- Energy stored in the bonds
What happens if delta U > 0?
Energy of system increases.
What happens if delta U < 0?
Energy of system decreases.
What happens if q > 0?
System absorbs heat (endothermic)
What happens if q < 0?
System releases heat (exothermic)
What happens if w > 0?
Work done ON the system by surroundings.
What happens if w < 0?
Work done BY the system.
What are some extensive properties?
Heat and heat capacity
What are some intensive properties?
Temperature, specific heat capacity, and molar heat capacity
What quantities does heat depend on?
- Temp change of a substance
- Amount of a substance
- Nature of the substance
What is heat capacity, Q?
The amount of heat required to change a system temperature by 1 degree.
What is specific hear capacity, c?
The amount of heat absorbed per unit mass of the material when its temperature increases by 1 degree.
What is molar heat capacity, C?
The amount of heat required to raise 1 mol by 1 degree.
What is the calorimeter?
An isolated system where no energy or matter is exchanged with surroundings. Specifically, it is used to measure the heat released during a reaction.
What are the two most common types of pressure-volume work?
- Work done BY a gas (expansion)
- Work done TO a gas (compression)
What happens when the Pext < Pint?
Gas will expand, forcing the piston to perform work on its surroundings.
Vi < Vf
What happens when the Pext > Pint?
Gas will be compressed, and the surroundings will perform work on the system.
Vi > Vf
What is enthalpy (H)?
The measure of energy in a thermodynamic system.
What is entropy (S)?
It is a measure of how energy is distributed to, from, or within a system as a function of temperature.
It is closely related to probability.
Does the entropy of a system increase if the kinetic energy of a system is increased?
Yes , the higher the KE, the more motion, which means more disorder.
What is the second law of thermodynamics?
All spontaneous processes produce an increase in the entropy of the universe.
What is the third law of thermodynamics?
The entropy of a pure, perfect crystal at 0K is 0. ( There is no disorder in a perfect system with no atomic motion)
What happens if heat is transferred from the surroundings?
- Tsur decreases
- Ssur < 0
What happens if heat is transferred to the surroundings?
- Tsur increases
- Ssur > 0
What is free energy (G)?
It is used to determine how systems change and how much work they can produce.
What happens if G < 0?
The reaction is spontaneous.
What happens if G = 0?
The reaction is in equilibrium.
What happens if G > 0?
The reaction is not spontaneous.
What happens |H| > |TS|?
The reaction is enthalpy driven.
What happens |H| < |TS|?
The reaction is entropy driven.
What are the x and y components, what is the equation, of temperature dependence graph?
x = 1/T
y = lnK
lnK = - H/R 1/T + S/R
What is an intensive property?
Properties that DO NOT depend on quantity or mass.
What is an extensive property?
Properties that DO depend on quantity or mass.
