unit 7-8

• Scientific studies depend on quantitative measurements. Each measurement has a number and unit that indicates how the measurement was done (in inches, miles, or meter)
• In order for scientists to communicate their results in an understandable form to colleagues all over the world, a standard unit was adopted for each type of measurement
• The international system (SI) of units is based on the metric system
• The Seven SI base Units

  • Mass (kilogram, kg)
  • Length (meter, m)
  • Temperature (Kelvin, K)
  • Amount of substance (mole, mol)
  • Time (second, s)
  • Electric current (Ampere, A)
  • Luminous intensity (candela, Cd)
• Other SI units are derived from these base units
• SI units are modified by prefixes

  Most common conversions are: mg, g, and kg; mL and L
• Convert


  • 253 mg = 0.253 g
  • 3.6 kg = 3600 g
  • 0.0587 L = 58.7 mL
  • 100.0 mL = 0.1000 L
  • 0.48 L = 480 cm3
• Volume


  SI unit is m3, but commonly use L or mL in chemistry; in Health Sciences it's common to use cc (cubic centimeter); Volume = length x width x height
• Mass


  Amount of matter in an object; measured using a balance comparing a known mass to an unknown mass; does not change when an object's location changes
• Weight


  Pull of gravity on an object; measured on a scale; changes when an object's location changes
• Density


  Mass of a substance divided by its volume; d = m/v
• Temperature


  Measure of how hot or cold an object is; units include Fahrenheit, Celsius, Kelvin, Rankine (rarely used)

  
• Kelvin temperature scale


  T(K) = T(°C) + 273.15 K

  
• Pressure


  Force exerted per unit area by gas molecules as they strike the surfaces around them; common units include Pascal (Pa), pounds per square inch (psi), Torr (mmHg), Bar, centimeter H2O (cm H2O), Atmosphere (atm)

  
• Normal atmospheric pressure at sea level is 101,325 Pa

  
• Common Pressure Units


  • Pascal (Pa)
  • Pounds per square inch (psi)
  • Torr (mmHg)
  • Bar
  • Centimeter H2O (cm H2O)
  • Atmosphere (atm)
• Convert CO2 gas pressure of 11.2 psi to bars, mmHg and atm

  • 0.772 bar
  • 579 mmHg
  • 0.762 atm
• Solids


  • Particles tightly packed together; constant volume and constant shape; least compressible; lowest kinetic energy; strongest intermolecular forces; highest density
• Liquids


  • Particles not fixed in place; constant volume but no constant shape; higher compressibility than solids; higher kinetic energy than solids; weaker intermolecular forces than solids; lower density than solids

  
• Gases


  • Lots of space between particles; no constant volume and no constant shape; most compressible phase; most kinetic energy; weakest intermolecular forces; lowest density
• The air we breathe is a mixture of different gases
• Major Constituents of Dry Air

  • Nitrogen (78%)
  • Oxygen (21%)
  • Argon (0.9%)
  • Carbon dioxide (0.04%)
• Humidity


  Amount of water vapor in the air; indicates likelihood of precipitation, dew, or fog; higher humidity reduces effectiveness of sweating and body cooling
• Absolute humidity


  Water content of air at a given temperature expressed in grams per cubic meter (g/m3); changes as temperature or pressure changes
• Relative humidity


  Expressed as a percentage (%); depends on both water content and temperature; expression of how much moisture air may have at a given temperature

  
• Conditions for gas volume

  • STPD: Standard Temperature (0°C) and Pressure (760mmHg) Dry
  • ATPS: Ambient Temperature (room temperature) and Pressure (760mmHg, depending on altitude) Saturated with water vapour
  • BTPS: Body Temperature (37°C) and Pressure (760mmHg) Saturated with water vapor

  
• Humidex


  Effect calculated to account for the combined effect of temperature and humidity on the rate of evaporation of moisture from the skin and therefore cooling of the body
• Absolute humidity


  Water content of air at a given temperature expressed in gram per cubic meter (g/m3)
• Relative humidity


  Expressed as a percentage (%), depends on both water content and temperature, an expression of how much moisture air may have at a given temperature

  
• Conditions for gases


  • STPD: Standard Temperature (0°C) and Pressure (760mmHg) Dry
  • ATPS: Ambient Temperature (room temperature) and Pressure (760mmHg, depending on altitude) Saturated with water vapour
  • BTPS: Body Temperature (37°C) and Pressure (760mmHg) Saturated with water vapor

  
• In future courses you will convert between these conditions to determine O2 consumption, CO2 production and lung volumes
• Gas Laws


  • Boyle's Law
  • Charles's Law
  • Gay-Lussac's Law
  • Combined Gas Law
  • Avogadro's Law
  • Ideal Gas Law
  • Dalton's Law
  • Graham's Law
• Boyle's Law


  The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure
• Calculation with Boyle's Law

  1. Given: V2=?, V1=8.0L, P1=550mmHg, P2=2200mmHg

  2. P1V1 = P2V2

  3. V2 = 2.0L
• Charles's Law


  The volume of a fixed amount of gas at constant pressure is directly proportional to its Kelvin temperature
• Calculations Using Charles's Law

  1. Given: V2=?, V1=785 mL, T1=21°C, T2=0°C

  2. V1/T1 = V2/T2

  3. V2 = 729 mL
• Gay-Lussac's Law


  The pressure of a fixed amount of gas at constant volume is directly proportional to its Kelvin temperature
• Combined Gas Law


  P1V1/T1 = P2V2/T2
• Concept Check: Oxygen gas


  1. Given: P1=15200 kPa, V1=50.0 L, T1=293.15 K, P2=102 kPa, T2=298.15 K

  2. P1V1/T1 = P2V2/T2

  3. V2 = 7.58 x 10^3 L
• Avogadro's Law


  The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas