9.2 Pressure and Its Units
Notes
Pressure is force per area. Gas pressure comes from particles colliding with the container walls.
- More collisions or harder collisions mean higher pressure.
- Units: $1 \text{ atm} = 760 \text{ mmHg} = 760 \text{ torr} = 101.3 \text{ kPa}$.
- A barometer measures air pressure. Standard pressure at sea level is 1 atm.
- Example: $\displaystyle 380 \text{ mmHg} \times \frac{1 \text{ atm}}{760 \text{ mmHg}} = 0.500$ atm.
- Gas law temperatures must be in kelvins: $K = °C + 273$.
Practice
Convert 202.6 kPa to atmospheres.
$\displaystyle \frac{202.6}{101.3} = 2.00$ atm.
Convert 0.750 atm to mmHg.
$0.750 \times 760 = 570$ mmHg.
Gas pressure in a container is caused by:
Each collision pushes on the wall; together they make pressure.
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