Physical chemistry Test 1
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Relatino betwene work and energy
w = E_kf-E_ki
Energy posessed by a body by virtue of being in mostion
Energy posessed by a body by virtue of position
A specific segmentof hte world with deffinite boundaries on which we focus our attention
The part of the world immediately surrounding a system
System and its surroundings
Can transfer heat and material
Can only transfer heat
Can transfer neither heat nor matter
Not a function of quantity
Directly a function of quantity
Equation of state
An equation that describes the condition of a system as a function of intensive properties
The systems variables of state are not changing with respect to time
The kinetic energy of molecualr motion
Zeroeth law of thermodynamics
- If A and B are in thermal equilibrium
- And B and C are in thermal Equilibrium
- Then A and C are in thermal Equilibrium
Applies under Isothermic Conditrions. If temperature and nubmer of mols are held constant then PV=Constant
Temperature is held constant
Pressure is held constant
If Pressure and mols are fixed then V/T =Constant
3 Assumptions of ideal gas law
- 1) gas is assumed to be composed of individual particles whose actual dimensions are small in comparison to the distance between them.
- 2) These particles are in constant motion and therefore have kinetic energy.
- 3) Neither attractive nor repulsive forces exist between the particles.
Number of molecules present
Pressure in terms of mean square speed
Average Kinetic Energy of a molecule in a system
Pressure exerted by a single component of a gas mixture. Defined by molar fraction* pressure total
Grahms law of Effucsion
- How many collisions pe second does a molecule experieince
- units : 1/s
- How many colisions per unit of second per volume occur?
Mean free path
- How far a molecule travels before a collision
Most probable velocity. Peak of maxwell curve
- Compression factor
Repulsive forces dominate (b term from nonideal gas)
Attractive forces dominate (a term)
Van Der Waals equation
Uses a to account for attraction and b to account for repulsion
No change in Heat (Q)
Terms in the maxwell constant of dN/Ndu
- Maps likely distribution of particle velocities
- Accoutns for incremental volume in maxwell distribution sphere
Maxwell normalization factor
- NOrmalizes maxwell distribution by total molecules likely to be present
- Average speed of a molecule in system given by maxwell normalization factor. Actually less common than
Least common of the important speeds in maxwell distribution, this is the root mean square speed.
Average kinetic energy per molecule formula and function of
- e==.5mu2This is a function primarilly of temperature.
When u is not velocity, what is it? (fucking headache)
- Internal energy: the internal energy of a molecule is the sum of its heat and work
First law of thermodynamics
Energy can neither be created nor destroyed. Only moved.
What are the Five macroscopic properties
Pressure, Temperature, Volume, Mass, Enegy
What are state functions?
The macroscopic properties that define a substance
What happens if we fix 3 of the state functions
The other two are then known
What is path dependence?
A path dependent function is dependent on how one reaches a point. Using a mountain analogy: Height to reach a point is always constant, distance is a function of the route you take to reach tehat point.
Are state functions path dependent?
No. They are not. It is part of what makes them state functions.
Points at which without an external operator acting, a system will hold in a steady state over time.
3 Criteria for equilibrium state
The mechanical properties, chemical properties and temperature throughout a system must be uniform for something to be in an equilibrium state
Reversible vs Irreversible processes
If a system is changed slowly enough to maintain an equilibrium state, it is considered a reversible process.
Sign convention for heat (q)
If a system absorbs heat, q is positive. If a system loses heat, q is negative
Sign convention for work on a system (w)
- If work is done on a system (work flows in), then w is positive
- If work is done by a system (work flows out), then w is negative.
- Heat of system. function ot work and internal energy
What can we know about internal energy of a system over an operation
Its change. We do not know how much internal energy a system posesses, only how much it changes over time
What type of properties are heat and work
Path properties. They are dependent entirely on path and not functions of state. they are inexact integrals.
Nature of intenral energy (u): What are the 3 things that contribute
- 1) kinetic energy of motion of hte individual molecules
- 2) Potential eneryg that arise form interactions between molecules
- 3) Kinetic and potential energy of nuclei and elctorns with inthe individual molecules.
What are the four types of work
- Chemical: energy of breaking chemical bonds
- Elctrical: Work performed by current
- Mechanical : Gross work of physical motion of masses
- Osmotic: Transportation and concentration of chemicals
What is work defined as?
A force over distance. IE ENERGY
How do we define reversible work in thermodynamics? (Form and two notes)
- Note that if P is not constant, we must deffine it as a function of volume before doing this calculation.
- Note that dv implies an infintessimal volume change.
Is more work done through reversible or irreversible processes? What do graphs look like?
- If a process is reversible, it requires more work to do because pressure is assumed constant constant and graph of change is curved.
- If a process is irreversible, then less work is required as both pressure and volume are assuemd to change. Graph is straight drop of pressure and the straight change of volume.
Which type of process(Reversible or irreversible ) generates more heat? Why?
- We assume inc U to be constant.
- With this as a given and the realization that
- there will be more heat generated by irreversible work because there is less actual work done.
What is formula and assumption of irreversible work?
- Irreversible work is assumed to happen suddenly. Too suddenly to be considered incremental. As such, we use the final pressure to calcualte
When is work maximized?
When a process is reversible.
What happens to internal energy for an isochoric process?
It is only a function of change of heat as volume is 'fixed'
What is Enthalpy (H)?
- Enthalpy is a state function equal to :
- H= U + PV = internal energy + PRessure * Volume
- This deffinition is only valid if all work is PV work.
What is the change in heat (q)for a constant pressure system?
Endothermic process definition
- One in which q and w are positive.
- This implies that heat and work flow into system.
- This also implies that the surroundings will lose heat and feel colder.
One in which q and w are negative.This implies that heat and work flow out of the system. This also implies that the surroundings will gain heat and feel hotter in temperature.
What are the two forms of heat capacity and why do we have them?
- Isochoric: Constant Volume
- Isobaric: Constant Pressure
Heat capacity is not a state function. It fluctuates fased on sate functions and as suc hwe need to account for environmental conditions.
What should we know about Cv and what is its formula?
- This is isochoric heat capacity. It implies that there is a constant volume in system. In general, it is less like lab work/real systems.
- Due to the lack of change in volume, we asusme this to be purely a function of intenral energy
- Its formula is: Cv=
What should we know about CP and what is its formula?
- This is Isobaric heat capacity. While pressure is constant, volume may vary and we thus may need to account for work. As such it is a function of Enthalpy (H) and is far more common in the lab.
- Cp = \gr
What is heat capacity?
How much heat energy (Joules) a kilogram of a substance must absorb to increase by 1 K in temperature.
It varies with temperature and type of system.
How are Isochoric and Isobaric heat capacity related?
Cpm =Cvm +R
When can you use either form of heat capacity to find change in heat?
When working with an ideal gas, either form of heat capacity is equally valid.
What is formula for change in enthalphy?
What is formula for change in internal energy?
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