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Gases. Volume, Pressure & Temperature. Volume: Total space occupied by a substance The volume of a gas can either increase (expansion) or decrease (contraction) Volume of a gas increases when the number of moles of gas increases Volume of a gas increases when temperature increases - PowerPoint PPT Presentation
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Gases
Volume, Pressure & Temperature
Volume: Total space occupied by a substance
The volume of a gas can either increase (expansion) or decrease (contraction)
Volume of a gas increases when the number of moles of gas increases
Volume of a gas increases when temperature increases
Volume of a gas increases when pressure decreases
Volume, Pressure & Temperature
Volume: Total space occupied by a substance
Usually measured in L (liquids and gases)
1 cm3 = 1 mL
1 dm3 = 1 L = 1000 mL
1 m3 = 1000 L
Volume, Pressure & Temperature
Volume: Total space occupied by a substance
Indicate, in each pair, which object has a higher gas volume, and why (same gas always).
Volume, Pressure & Temperature
Pressure: Force applied per unit of area (P = F/A)
The pressure of a gas results from the collisions of the gas molecules with the walls of the container
Pressure of a gas increases when the number of moles of gas increases
Pressure of a gas increases when temperature increases
Pressure of a gas increases when volume decreases
Volume, Pressure & Temperature
Pressure: Force applied per unit of area (P = F/A)
Can be measured in different units
1 atm = 101.3 kPa *Standard Pressure
1 atm = 760 mm Hg
1 atm = 1013 mbar
Can be measured with a barometer (atmospheric pressure) or a manometer (gas pressure in closed container)
Volume, Pressure & Temperature
Pressure: Force applied per unit of area (P = F/A)
If the same person is wearing these shoes when stepping on somebody’s foot: which heel would exert more pressure? Why?
Volume, Pressure & Temperature
Pressure: Force applied per unit of area (P = F/A)
How could you lower the pressure applied by this truck on the road? Explain.
Volume, Pressure & Temperature
Temperature: Manifestation of average kinetic energy of molecules of a gas
Which gas is at a higher temperature? Explain.
Volume, Pressure & Temperature
Boyle’s law: At constant temperature, the volume of a given quantity of gas is inversely proportional to its pressure
PV = k (k: constant)
or
P1V1 = P2V2
Volume, Pressure & Temperature
Example: You need to put the equivalent of 400 L of air at standard pressure to go scuba- diving. If your tank’s capacity is only 11.4 L, what pressure will be needed in it assuming that temperature is constant?
Volume, Pressure & Temperature
Volume, Pressure & Temperature
Volume, Pressure & Temperature
Volume, Pressure & Temperature
Kelvin’s absolute temperature:
At T = 0°C, T = 273K T(K) = T(°C) + 273
Freezing point of Water:
T(K) = T(°C) + 273
T(K) = 0°C + 273
T(K) = 273K
Boiling point of Water:
T(K) = T(°C) + 273
T(K) = 100°C + 273
T(K) = 373K
Volume, Pressure & Temperature
Charles’s law: At constant pressure, the volume of a given quantity of gas is directly proportional to its temperature
V/T (K) = k (k: constant)
or
V1 / T1(K) = V2 / T2 (K)
*T(K): temperature in Kelvin T(K) and n must be constant
Volume, Pressure & Temperature
Combining Boyle’s & Charles’s law: At constant volume, the pressure of a given quantity of gas is directly proportional to its temperature
P/T (K) = k (k: constant)
or
P1 / T1(K) = P2 / T2 (K)
*T(K): temperature in Kelvin T(K) and n must be constant
Volume, Pressure & Temperature
When temperature increases in a room (external factor):
_The volume (internal factor) of a gas trapped in a container increases, as molecules will move faster, collisions will increase and expansion will occur.
_The pressure (internal factor) will also increase because molecules will move faster and therefore collide with walls of recipient with higher force.
It all leads to an EXPLOSION!
Volume, Pressure & Temperature
Example: The volume of a given gas sample is 1.56L at -70°C. What will its volume be at 2°C if the pressure of the system remains constant?
Volume, Pressure & Temperature
Yes. The speed (and thus kinetic energy) of gas molecules has increased as a result of the increase in temperature
Volume does not change (can)
Pressure increased as the energy given to molecules (by the increase of temperature) increased their velocity (Ek) and so their collisions with walls
would increase, thus increasing pressure (P=F/A)
No, it does not. It only applies when volume is allowed to change as a result of a change in temperature, at constant pressure.