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Important InformationImportant Information
• What is STP?• Standard Temperature and Pressure.• 1 atm pressure and 273 Kelvin• What are standard conditions?• Pressure is still 1 atm, but the
temperature is 25 degrees C or 298 K
• What is STP?• Standard Temperature and Pressure.• 1 atm pressure and 273 Kelvin• What are standard conditions?• Pressure is still 1 atm, but the
temperature is 25 degrees C or 298 K
UnitsUnits
• Units are very important in this chapter.
• One must be consistent or be incorrect.• All temperature must be in Kelvin.• °C + 273 = Kelvin• Pressure may be in one of these
choices:• 1 atm 760 mmHg• 760 torr 101.3 kPa
• Units are very important in this chapter.
• One must be consistent or be incorrect.• All temperature must be in Kelvin.• °C + 273 = Kelvin• Pressure may be in one of these
choices:• 1 atm 760 mmHg• 760 torr 101.3 kPa
Effusion and DiffusionEffusion and Diffusion
EffusionEffusion DiffusionDiffusion• The rate at which a
gas moves from area of high concentration to low concentration
• The rate at which a gas moves from area of high concentration to low concentration
• The passage of a gas through a tiny orifice.
• The passage of a gas through a tiny orifice.
Boyles LawBoyles Law
• http://en.wikipedia.org/wiki/Boyle's_law• Pressure and Volume are inversely
proportional when temperature is constant.
• As Pressure increases, Volume decreases and visa versa.
• P1V1=P2V2
• If a system with a pressure of 5 atm and 45 ml is compressed to 30 ml, what is the new pressure?
• http://en.wikipedia.org/wiki/Boyle's_law• Pressure and Volume are inversely
proportional when temperature is constant.
• As Pressure increases, Volume decreases and visa versa.
• P1V1=P2V2
• If a system with a pressure of 5 atm and 45 ml is compressed to 30 ml, what is the new pressure?
Boyle’s LawBoyle’s Law
• P1 V1= P2 V2
• 5 atm 45 ml = X 30 ml• X=(5atm*45ml)/30ml• X= 7.5 atm
• P1 V1= P2 V2
• 5 atm 45 ml = X 30 ml• X=(5atm*45ml)/30ml• X= 7.5 atm
Charles’ LawCharles’ Law
• http://en.wikipedia.org/wiki/Charles's_law
• Volume and Temperature are directly proportional when pressure is constant.
• As Volume increases, so does Temperature.
• V1 = V2• T1 T2• What happens to a 1 liter balloon at 25
degrees Celsius if the temperature is reduced to 0 degrees Celsius?
• http://en.wikipedia.org/wiki/Charles's_law
• Volume and Temperature are directly proportional when pressure is constant.
• As Volume increases, so does Temperature.
• V1 = V2• T1 T2• What happens to a 1 liter balloon at 25
degrees Celsius if the temperature is reduced to 0 degrees Celsius?
Charles’ LawCharles’ Law
• V1 1 liter = V2 X• T1 25°C T2 0°C• Temperature must be in Kelvin!!!! C+
273=K• V1 1 liter = V2 X• T1 298 K T2 273 K• X= (1 L*273 K)/298K• X=0.916 L new volume
• V1 1 liter = V2 X• T1 25°C T2 0°C• Temperature must be in Kelvin!!!! C+
273=K• V1 1 liter = V2 X• T1 298 K T2 273 K• X= (1 L*273 K)/298K• X=0.916 L new volume
Gay-Lussac’s LawGay-Lussac’s Law
• Pressure and Temperature are directly proportional when the volume remains constant.
• The pressure increases as the temperature in kelvin increases.
• Pressure and Temperature are directly proportional when the volume remains constant.
• The pressure increases as the temperature in kelvin increases.
Gay-Lussac’s LawGay-Lussac’s Law
• What is the new pressure if a ridged container at 1 atm and 25 °C is heated to 75° C?
• P1 1 atm = P2 X• T1 25°C T2 75°C• Temperature must be in Kelvin!!!! C+
273=K• P1 1 liter = P2 X• T1 298 K T2 348 K
• What is the new pressure if a ridged container at 1 atm and 25 °C is heated to 75° C?
• P1 1 atm = P2 X• T1 25°C T2 75°C• Temperature must be in Kelvin!!!! C+
273=K• P1 1 liter = P2 X• T1 298 K T2 348 K
Combined Gas LawCombined Gas Law
• Pressure and volume are inversely proportional. Both Pressure and Volume are directly proportional to temperature.
• We can combine Charles’, Boyle’s and Gay-Lussac’s Law to form the Combined gas law.
• Pressure and volume are inversely proportional. Both Pressure and Volume are directly proportional to temperature.
• We can combine Charles’, Boyle’s and Gay-Lussac’s Law to form the Combined gas law.
Combined Gas LawCombined Gas Law
• You have an expandable syringe holding a volume of 20ml at STP.
• What is the new volume at Standard Conditions?
• P1=1 atm * V1 =20mL P2=1 atm * V2 =X
• T1 = 273 K = T2 = 298 K
• X= 21.8 ml
• You have an expandable syringe holding a volume of 20ml at STP.
• What is the new volume at Standard Conditions?
• P1=1 atm * V1 =20mL P2=1 atm * V2 =X
• T1 = 273 K = T2 = 298 K
• X= 21.8 ml
Ideal Gas LawIdeal Gas Law
• The main difference with the ideal gas law is that now we take the number of moles of gas into consideration.
• All previous gas laws had a constant amount of gas.
• In the ideal gas law, the number of moles of a gas is also a variable.
• To do this the equation requires a conversion factor called, R.
• The main difference with the ideal gas law is that now we take the number of moles of gas into consideration.
• All previous gas laws had a constant amount of gas.
• In the ideal gas law, the number of moles of a gas is also a variable.
• To do this the equation requires a conversion factor called, R.
Ideal Gas LawIdeal Gas Law
• PV=nRT• Pressure times Volume equals the
number of moles times the gas constant times the Temperature in Kelvin.
• There are many versions of the Gas constant, R. We will use only two.
• R= 0.0821 (L*atm)/(mol*Kelvin)• R= 8.31 (L*kPa)/(mol*Kelvin)
• PV=nRT• Pressure times Volume equals the
number of moles times the gas constant times the Temperature in Kelvin.
• There are many versions of the Gas constant, R. We will use only two.
• R= 0.0821 (L*atm)/(mol*Kelvin)• R= 8.31 (L*kPa)/(mol*Kelvin)
Units and the Ideal Gas Law
Units and the Ideal Gas Law
• The units of your problem must match the units in your gas constant, R.
• If they do not you need to convert those units that do not match.
• Example:• I have 20 grams of neon gas at 760
mmHg and 0° C. What is the volume of this gas?
• The units of your problem must match the units in your gas constant, R.
• If they do not you need to convert those units that do not match.
• Example:• I have 20 grams of neon gas at 760
mmHg and 0° C. What is the volume of this gas?
AnswerAnswer
• Which R? • I chose R=0.08206
(L*atm)/(mole*Kelvin)• First we need moles of gas not grams• 20 g/(20g/mol)=1 mole of Neon• Pressure from mmHg to atm• 760 mmHg*(1 atm/760 mmHg)= 1 atm• Temperture from Celsius to Kelvin• 0° C +273=273 Kelvin
• Which R? • I chose R=0.08206
(L*atm)/(mole*Kelvin)• First we need moles of gas not grams• 20 g/(20g/mol)=1 mole of Neon• Pressure from mmHg to atm• 760 mmHg*(1 atm/760 mmHg)= 1 atm• Temperture from Celsius to Kelvin• 0° C +273=273 Kelvin
Answer continuedAnswer continued
• PV=nRT• 1atm(V)= [1
mol*0.0821(L*atm)/(mol*K)]273K• V=[1mol*0.0821 (L*atm/mol*K)*273K]/1atm• Cancel your units and do the math:• V=0.0821 L/273• V= 22.4 L• In fact, all gases at STP occupy 22.4 L/mol
• PV=nRT• 1atm(V)= [1
mol*0.0821(L*atm)/(mol*K)]273K• V=[1mol*0.0821 (L*atm/mol*K)*273K]/1atm• Cancel your units and do the math:• V=0.0821 L/273• V= 22.4 L• In fact, all gases at STP occupy 22.4 L/mol
How to determine which to use
How to determine which to use
• Ideal or Combined?• Does the problem mention a change in
either Temperature, Pressure or Volume?
• Combined Gas Law!• Does the problem give or ask for the
number of grams of a gas or the number of moles of a gas?
• Ideal Gas law!
• Ideal or Combined?• Does the problem mention a change in
either Temperature, Pressure or Volume?
• Combined Gas Law!• Does the problem give or ask for the
number of grams of a gas or the number of moles of a gas?
• Ideal Gas law!
Dalton’s Law of Partial Pressures
Dalton’s Law of Partial Pressures
• In a mixture of gases, each gas has its own partial pressure. The total pressure in the container is the sum of the partial pressures.
• PT=P1+P2+P3…Pn• It is important that all the pressures are
in the same units before adding them together!
• In a mixture of gases, each gas has its own partial pressure. The total pressure in the container is the sum of the partial pressures.
• PT=P1+P2+P3…Pn• It is important that all the pressures are
in the same units before adding them together!
Graham’s Law of EffusionGraham’s Law of Effusion
• Larger molecules will migrate slower than a smaller molecule under a constant temperature.
• This is in direct violation of the KMT.
• REAL GASES have significant size
• Larger molecules will migrate slower than a smaller molecule under a constant temperature.
• This is in direct violation of the KMT.
• REAL GASES have significant size
Graham’s LawGraham’s Law
• Which of these gases will effuse faster, He, Ne, Xe?
• When all gases are at the same temperature, they have the same kinetic energy. Therefore the smallest gas, Helium, will effuse faster.
• Which of these gases will effuse faster, He, Ne, Xe?
• When all gases are at the same temperature, they have the same kinetic energy. Therefore the smallest gas, Helium, will effuse faster.