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Gas Laws Boyles Law Charless Law Gay-Lussac Combined Gas Law.

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Presentation on theme: "Gas Laws Boyles Law Charless Law Gay-Lussac Combined Gas Law."— Presentation transcript:

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2 Gas Laws Boyles Law Charless Law Gay-Lussac Combined Gas Law

3 Properties of Gases V = volume of the gas (liters, L) T = temperature (Kelvin, K) P = pressure (atmospheres, atm) n = amount (moles, mol) Gas properties can be modeled using math. Model depends on:

4 Pressure - Temperature - Volume Relationship P T V Gay-Lussacs P T CharlesV T P T V Boyles P 1V1V

5 Pressure - Temperature - Volume Relationship P T V Gay-Lussacs P T CharlesV T Boyles P 1V1V ___ P n V

6 Pressure and Balloons A B = pressure exerted ON balloon A = pressure exerted BY balloon B When balloon is being filled: P A > P B When balloon is filled and tied: P A = P B When balloon deflates: P A < P B

7 When the balloons are untied, will the large balloon (A) inflate the small balloon (B); will they end up the same size or will the small balloon inflate the large balloon? Why? Balloon Riddle A B C

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9 Robert Boyle Robert Boyle, an Irish chemist ( ), performed the first quantitative experiments on gases used a j- shaped tube to study the relationship between the pressure of the trapped gas and its volume.

10 Boyles Law Boyles Law states that at constant temperature (and constant number of gas molecules) the volume of a fixed amount of gas is inversely proportional to its pressure. Boyles Law: P 1 V 1 = P 2 V 2

11 Boyle Proves Changes in Pressure cause Changes in Volume As the pressure in a closed system (like a piston) decreases, the volume of the gas inside the system increases. The pressure in the system decreases exponentially. Proving an indirect relationship.

12 Example: Sulfur dioxide (SO 2 ), a gas, that plays a central role in the formation of acid rain, is found in the exhaust of automobiles and power plants. Consider a 1.53 L sample of gaseous SO 2 at a pressure of 5.6 kPa. If the pressure is changed to 15 kPa at a constant temperature, what will be the new volume of the gas?

13 Solution: P 1 V 1 = P 2 V 2 P 1 = 5.6 kPaP 2 = 15 kPa V 1 = 1.53 LV 2 = ? Rearrange the formula to isolate V 2. P 1 V 1 = (5.6 kPa)(1.53 L) = O.571 L P 2 (15 kPa)

14 Does Boyles law really work? Since Boyles experiments (only three centuries of technological advances!) we have found that his law only holds precisely at very low pressures. We describe a gas that strictly follows Boyles law an ideal gas.

15 Jacques Charles In the century following Boyle, a French physicist, Jacques Charles ( ), was the first person to fill a balloon with hydrogen gas and who made the first solo balloon flight.

16 Charless Law Charless Law states that at constant pressure (and constant number of gas molecules) the volume of a fixed amount of gas is directly proportional to its absolute temperature. *All gas laws must be calculated with Kelvin temperature!

17 Volume vs. Temperature: Charles Law Notice the linear relationship. This relationship between temperature and volume describes a direct relationship. This means when temperature increases, so does the volume.

18 The importance of 0 Kelvin At temperatures below 0 K, the extrapolated volume of gases would be negative. The fact that a gas cant have a negative volume tells us 0 K has a special significance. Absolute temperature is measured in Kelvins. At 0 K, all motion of any atom or bond ceases, therefore producing no energy. Temperatures of approximately K have been produced in laboratories, but 0 K has never been reached.

19 Example: A sample of a gas at 15°C and 1 atm has a volume of 2.58 L. What volume will the gas occupy at 38°C and 1 atm? (NOTE: The pressure did not change. So you do not need to worry about it!)

20 Solution: V 1 = V 2 Dont forget to convert °C to K T 1 T 2 V 1 = 2.58LV 2 =? T 1 = 15°C=288K T 2 = 38°C=311K Rearrange to solve for V 2. V 1 T 2 = (2.58L)(311K) = 2.79 L T 1 (288K)

21 Gay-Lussac Joseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries – 1850 Charles's law, describing how gases tend to expand when heated, was formulated by Joseph Louis Gay-Lussac in 1802, but he credited it to unpublished work by Jacques Charles.

22 Gay-Lussacs Gas Law The pressure of a fixed mass and fixed volume of a gas is directly proportional to the gas's temperature. *All gas laws must be calculated with Kelvin temperature!

23 The Combined Gas Law The combined gas law was derived from Boyles and Charless work. A direct relationship was observed. As temperature increased, volume increased. As volume increased pressure increased. This resulted in a combined formula to calculate changes observed in a gas due to changes in either temperature, pressure or volume.

24 Combined Gas Law Equation By combining the equation for Boyles Law and Charless Law. We derive the Combined Gas Law Equation where:

25 Example: A sample of a gas at 15°C and 2.0 atm has a volume of 2 mL. What volume will the gas occupy at 38°C and 1 atm?

26 Solution P 1 V 1 = P 2 V 2 Dont forget to convert Temperatures! T 1 T 2 P 1 = 2 atmP 2 = 1 atm V 1 =2 mLV 2 =? T 1 =15 °C=288K T 2 =38°C=311K Rearrange to solve for V 2 ! V 2 = P 1 V 1 T 2 = (2 atm)(2 mL)(311K) = 4.32 mL T 1 P 2 (288K)(1 atm)

27 Summary: Boyles Law – Inverse relationship when P V and if P V Charless Law -- Direct relationship When V T and if V T Gay-Lussac Law -- Direct relationship When P T and if P T


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