Key Terms
Pressure
Force exerted per unit area. P = F/A
Two ways to increase pressure
Increase force OR decrease area. Two ways to decrease pressure: decrease force OR increase area.
Barometer
Measures atmospheric pressure. Glass tube sealed at one end, filled with mercury, inverted into a dish of mercury.
Hydrostatic pressure formula
P = h x rho x g h = height of fluid; rho = density; g = gravitational acceleration
Manometer
Measures pressure of a trapped gas sample.
If gas side is higher
P(gas) = P(atm) - h
If atm side is higher
P(gas) = P(atm) + h
Same principle applies to scuba diving
As a diver ascends and pressure drops, air in the lungs expands.
STP
273.15 K (0 degrees C) and 1 atm (101.325 kPa)
Partial pressure of a component
P(A) = X(A) x P(total)
Path for gas stoichiometry
1. Use PV = nRT to find moles of given gas (if V, P, T provided).
SHORTCUT when T and P are the same for both gases
At constant T and P, volume ratios equal mole ratios. The coefficients in the balanced equation directly give you volume
Example
N2 + 3H2 --> 2NH3 1 volume N2 reacts with 3 volumes H2 to produce 2 volumes NH3, as long as all volumes are measured at
Diffusion
Molecules spreading from high concentration to low concentration through space. What you experience when a smell travels
Effusion
Molecules escaping through a tiny opening (pinhole) into a vacuum.