Temperature Unit Kelvin (K) Kelvin = °C + 273
Jan 12, 2016
Temperature
Unit Kelvin (K)
Kelvin = °C + 273
Temperature
Convert 45°C to Kelvin
45°C + 273= 318 K
Temperature
Absolute zero – 0 K Molecules stop moving
Question: what is absolute zero temperature in Celsius?
-273°C
Volume
Units: mL L
Amount
Units grams moles
Gas Laws
Each gas law relates the 4 variables: Pressure Temperature Volume Amount
For the next 4 gas laws, amount is not a factor
We will only pay attention to P, T, & V
Boyles’ Law: P/V relationship
Defn – at constant T, volume of a fixed amount of gas varies inversely with pressure inversely – as one variable increases,
other variable decreases
P
V
Boyle’s Law
FormulaP1V1 = P2V2
P1 & V1 are initial conditions
P2 & V2 are final conditions
Boyle’s Law
A balloon filled with helium gas has a volume of 500 mL at 1.00 atm. When it rises to a higher altitude, the pressure is reduced to 0.50 atm. If the temperature is constant, what is the volume of the balloon?
1000 mL
Charles’ Law: V/T relationship
Defn – at constant P, volume of fixed amt of gas varies directly with Kelvin temp Directly – as one variable increase,
the other increases
V
T
Charles’ Law Formula
V1 & T1 are initial conditions V2 & T2 are final conditions
2
2
1
1
T
V
T
V
Charles’ Law
A helium balloon has a volume of 2.75 L at 20°C. On a cold day, the balloon is placed outside where it shrinks to 2.46 L. What is the temperature outside?
262 K
Gay-Lussac’s Law: P/T relationship
Defn – at constant V, pressure of fixed amt of gas varies directly with Kelvin temp Directly – as one variable increase,
the other increases
P
T
Gay-Lussac’s Law Formula
P1 & T1 are initial conditions P2 & T2 are final conditions
2
2
1
1
T
P
T
P
Gay-Lussac’s Law
Before a trip from Sugar Land to South Padre, the pressure in an automobile tire reads 2.1 atm at 27°C. Upon arriving in Padre, the gauge reads 2.3 atm. What is the temperature in South Padre?
329 K
Combined Gas Law: P/T/V Defn – relationship between P,V, & T
of fixed amount of gas Formula
2
22
1
11
T
VP
T
VP
Combined Gas Law
The volume of a gas is 27.5 mL at 22.0°C and 740 mm Hg. What will be its volume at 15°C and 755 mm Hg?
26 mL
Avogadro’s Principle
Defn – equal volumes of gases at same temp and pressure contain equal number of molecules- the size of the molecule does not influence the volume a gas occupies
- for example, 1000 relatively large Kr gas molecules occupies the same volume as 1000 smaller He gas molecules
Molar Volume of a Gas
Molar Volume – volume that one mole of a gas occupies at STP (0°C, 1 atm)
1 mole = 22.4 L
Molar Volume of a Gas
Ex prob #1: calculate the volume 0.881 mol H2 will occupy at STP.
0.881 mol H2
0.881 mol H2 x 22.4 L H2
1 mol H2
= 19.7 L H2
Molar Volume of a Gas
What is the mass of 0.0752 L of oxygen gas at STP? 0.0752 L O2
0.0752 L O2 x 1 mol O2
22.4 L O2
0.0752 L O2 x 1 mol O2 x 32 g O2
22.4 L O2 1 mol O2
= 0.107 g O2
Ideal Gas Law
Defn – relationship between P,V,T and # of moles, n
FormulaPV = nRT
Ideal Gas Law
Defn – relationship between P,V,T and # of moles, n
FormulaPV = nRT
ideal gas constant
Ideal Gas Constant 3 different R
constants
R = 0.0821 L·atm mol·K
= 62.4 L· mm Hg mol·K
= 8.314 L·kPa mol·K
pay attention to what unit of pressure is given in problem to use the appropriate R
Ideal Gas Law
Ex prob 1: what is the volume of 0.250 moles of oxygen gas at 20°C and 740 mm Hg?
which R do we use?
6.18 L O2
Ideal Gas Law
Ex prob 2: calculate the pressure, in atm, of 4.75 L NO2 containing 0.86 mol at 27°C.
4.46 atm
Ideal Gas Law
Ex prob 3: calculate the grams of N2 present in a 0.600 L sample kept at 1.0 atm and 22°C.first determine # of moles
0.025 mol N2
convert to grams0.70 g N2