4B: importance of fluids for the circulation of blood, gas movement, and gas exchange (genchem: gas phase)

Question 1

Absolute Temp (K)-Kelvin

Absolute Zero= C?

Kelvin to Celsius Convert?

Thermal energy vs temp?

Answer 1

• Absolute zero = -273 deg C
• Kelvin to Celsius converter
  
  • K = C + 273, absolute zero = 0 K
• ​Temperature = KE per mole of molecules, intensive property
• Temp vs. thermal energy:​
  • thermal energy is extensive, describes total energy of molecular motion
  • Temperature is intensive, describes average energy per unit

Question 2

Pressure, simple mercury barometer

Translational KE

Answer 2

• pressure: KE of a group of molecules per volume occupied, intensitve property
• Translational KE = energy due to motion from one location to another

Question 3

Mercury barometer:

procedure

rationale

Answer 3

• Mercury barometer: way of measuring atmospheric pressure
• Procedure

1. Invert a test tube filled with mercury on an uncovered bath open to the atmosphere
2. Some mercury falls into the bath, some stays in the test tube
3. Plug the height of the remaining mercury into the equation: Patm = pgh
   
   1. Patm = atmospheric pressure, p = density of mercury, g = 9.8 m/s2, h = height of mercury remaining in test tube

• Rationale: pressure of the atmosphere pushing DOWN on the bath is related to how much mercury is left in the test tube
• mmHg = how high in millimeters the mercury level is

Question 4

Molar Volume at 0 deg. C and 1 atm=?

• one mole of any gas will occupy how many liters at STP?

Answer 4

• molar volume=22.4 L/mol
  
  • ​at STP, one mole of any gas will occupy 22.4 liters

Question 5

Ideal gas 4 qualities

Answer 5

Definition: 4 qualities

1. Gas molecules have no size, zero molecular volume (not the same as the size of the container)
2. Gas molecules don’t exert attractive or repulsive forces on one another (no IMF’s)
3. Gas molecules have completely elastic collisions
4. Average KE per gas molecule is proportional to the overall temperature of the gas

Question 6

Ideal Gas Law: PV = nRT

Answer 6

• Unless told otherwise, MCAT gases are ideal
• T: the temperature of the gas (taken in K for ideal gas)
  
  • Ideal gases are in thermal equilibrium with surroundings. Both gas and surroundings are at same temperature
• V: the volume of the container the gas is in
  
  • 2 types of containers:

1) Flexible: volume of container changes depending on the temperature, pressure, and amount of gas within

2) Rigid: volume is fixed and cannot change

• P: pressure exerted by the gas on the container
  
  • For a flexible container, P = the external pressure
  • If it didn’t, the container would stretch or shrink until P = external temperature
  • Pressure of gas in the atmosphere is always 1 atm

Question 7

Boyle’s Law:

Answer 7

• PV = constant
• Pressure and volume are inversely proportional to keep PV a constant value

Question 8

Charles’ Law

Answer 8

• V/T = constant
• Increase in temperature leads to greater KE and speed per molecule. They speed up and start to collide with each other more, increasing the volume
• Volume and temperature are directly proportional to keep V/T constant

Question 9

Avogadro’s Law:

Answer 9

• V/n=constant

Question 10

Kinetic Molecular Theory of Gases

Answer 10

• Heat capacity at constant volume and at constant pressure
  
  • Effect of constant volume and pressure on heat capacity
    
    • Constant volume: if V is constant, a system can do no PV work so all E exchange must be in the form of heat. This means less E is needed to get to capacity required to change T by 1 C or K.
    • Constant pressure: P is constant so V can change. This means the system can do PV work as well so some E put in will go towards raising the V instead of changing the T. More E required to get to capacity
    • C_constant V < C_constnat P

Question 11

Boltzmann’s Constant

Answer 11

• used to calculate average KE of a single molecule in a given fluid, k = 1.38*10-23 J K-1 § K.E. = 3/2 RT
• R = ideal gas constant, T = temperature in K, K.E. = average KE per mole of molecules

Question 12

• Deviation of real gas behavior from Ideal Gas Law*
• Qualitative*
• Quantitative (van der waal’s equation)*

Answer 12

• Qualitative
  
  • Deviations occur when gas molecules get close together
    
    • B/c of volume of gas particles and electrostatic forces between gas particles (Coulombs Law)
  • Deviations caused by high pressures or low temperatures
• Quantitative (Van der Waals’ Equation)
  
  • ​P_real < P_ideal
    
    • Gas molecules exhibit mostly attractive forces on one another. Pulls gas molecules inwards, lowers collisions on container walls, and lowers P
  • V_real > V_ideal
    
    • Gas molecule size comes into play in a real gas. Volume of gas molecule increase the actual volume

Question 13

Partial Pressure, mole fraction

Answer 13

• In a mixture of gases, amount of pressure each gas contributes is proportional to how many molecules it contributes to the mixture
• Partial pressure: amount of pressure contributed by a single gas to a mixture
  
  • P_a = xaP_total
    
    • ​Pa = partial pressure of gas a, xa = molar fraction of gas a
• Rxns involving gases can have their equilibrium constant written in terms of partial pressures
  
  • ​K_p = partial pressures of products / partial pressure of reactants
  • K_p = Kc(RT)^Δn

Question 14

Vapor pressure

Vapor pressure and strength of bonds in a solution?

Answer 14

• Vapor pressure: pressure created by molecules above liquid surface at equilibrium
• Driven by entropy difference between liquid and gas phases (bigger difference–>liquid wants to assume lower entropy more–>higher vapor pressure)
• Molecules on liquid surface get enough KE to break off into open space above liquid
• Molecules in open space crash down into liquid
• Equilibrium is reached when rate of molecules leaving surface and molecules re-entering equals each other. Pressure at this equilibrium is vapor pressure
• High vapor pressure = weaker bonds in solution, positive heat of solution
• Low vapor pressure = stronger bonds in solution, negative heat of solution

Question 15

• Differences in vapor pressure and partial pressure of solute in open space causes evaporation and condensation
• Evaporation:
• Condensation:
• Boiling:

Answer 15

• Evaporation: partial pressure of solute is less than vapor pressure
• Condensation: partial pressure of solute is greater than vapor pressure
• Boiling: atmospheric pressure (sum of all partial pressures in open space) equals vapor pressure

Question 16

Vapor pressure is fixed at a given ______________ (only factor that matters)

Answer 16

• temperature

Question 17

Raoult’s Law

talk about nonvolatile solute

Answer 17

• For a nonvolatile solute (solute with no vapor pressure)
  
  • nonvolatile solute increases entropy of liquid phase while not increasing entropy of gas phase (doesn’t break off into open space)
    
    • ​This lowers the entropy difference between liquid and gas (the driving force for vapor pressure), thereby lowering vapor pressure
  • More nonvolatile solute = less vapor pressure
  • P_v = X_aP_a
    
    • _​Vapor pressure of solution=mole fraction of liquid “a” * vapor pressure of the pure liquid “a”

Question 18

Dalton’s Law relating a partial pressure to compostition

Answer 18

• Total pressure a gaseous mixture exerts is the sum of the partial pressure of each of its constituent gases