1. Gas Laws

2. Standard Temperature and Pressure (STP)
Standard temperature: 0°C or 273 K
Standard pressure: 1 atm, 760 mm Hg, or kPa

3. Boyle’s Law
The pressure of a dry gas is inversely proportional to its volume if the temperature is held constant.

4. Inverse Proportion
two terms related so that, if one term increases, the other term decreases

5. Boyle’s Law P , V
PV = k
P1V1 = P2V2

6. As pressure increases, volume decreases.
Chemistry textbook, p. 250

7. Chemistry textbook, p. 250

8. Sample Problem 1
A sample of gas occupies 352 mL at a pressure of 3.17 atm. If the P is reduced to 1.24 atm, what volume will result?
P1V1 = P2V2
(3.17 atm)(352 mL) = (1.24 atm)V2
900 mL = V2

9. Question
A sample of gas occupies 200 mL at a P of 2.15 atm. If the P is reduced to 1.25 atm, what is V2?
344 mL
537 mL
98 mL
89 mL

10. (2.15 atm)(200 mL) =
(1.25 atm) V2
430 mL = 1.25 V2
344 mL = V2

11. Question 2,175 mm Hg 225 mm Hg 339 mm Hg 1 mm Hg
A sample of gas is at a P of 700 mm Hg with a V of 300 mL. What P will increase the V to 932 mL?
2,175 mm Hg
225 mm Hg
339 mm Hg
1 mm Hg

12. (700 mm Hg)(300 mL) =
P2(932 mL)
210,000 mm Hg = 932 P2
225 mm Hg = P2

13. Charles’s Law
The volume and absolute temperature of a gas are directly proportional to one another if the pressure is held constant.

14. Direct Proportion
two terms related so that, if one term increases, the other term also increases

15. Charles’s Law V , T
= k V T V1 T1 V2 T2 =

16. As temperature increases, volume increases.
Chemistry textbook, p. 251

17. Chemistry textbook, p. 251

18. Sample Problem 2
If a sample of gas occupies 478 mL at 126 K, what volume will result if the gas is heated to 245 K?

19. Sample Problem 2 V1 T1 = V2 T2 (478 mL) (126 K) = V2 (245 K)
(478 mL)(245) = (126)V2
929 mL = V2

20. Sample Problem 3
If a sample of gas occupies 478 mL at 126°C, what volume will result if the gas is heated to 245°C?

21. Sample Problem 3 V1 T1 = V2 T2 (478 mL) (126°C) = V2 (245°C)
NOTE: T must be in K—add 273
(478 mL)(518) = (399)V2
621 mL = V2

22. Question
If a sample of gas occupies 232 mL at 321 K, what V will result if the gas it heated to 554 K?
134 mL
767 mL
400 mL
0.001 mL

23. 232 mL
321 K V2
554 K =
(232 mL)(554 K) = (321 K)V2
128,528 mL = (321)V2
400 mL = V2

24. Question
If a sample of gas occupies 112 mL at 313°C, what will be the T if the V becomes 52 mL?
REMEMBER KELVIN!
19 K
10 K
145 K
272 K

25. 112 mL
586 K =
52 mL T2
(112 mL)T2 = (586 K)(52 mL)
112 T2 = 30,472 K
T2 = 272 K

26. Gay-Lussac’s Law
The pressure of a confined gas is directly proportional to its absolute temperature if the volume is held constant.

27. Gay-Lussac’s Law P , T
= k P T P1 T1 P2 T2 =

28. As temperature increases, pressure increases at a constant volume.
Chemistry textbook, p. 253

29. Chemistry textbook, p. 253

30. Question 18 psi 33 psi 37 psi 68 psi
If a the P of a tire is 35 psi at 21°C, what will the P be if the T is raised to 41°C?
18 psi
33 psi
37 psi
68 psi

31. 35 psi
294 K =
314 K P2
(35 psi)(314 K) = (294 K)P2
10,990 psi = 294 P2
37.4 psi = P2

32. Combines Boyle’s law, Charles’s law, and Gay-Lussac’s law
Combined Gas Law
Combines Boyle’s law, Charles’s law, and Gay-Lussac’s law

33. Combined Gas Law
Boyle’s PV V T
Charles’s P T
Gay-Lussac’s

34. Combined Gas Law
P1V1 T1
P2V2 T2 =

35. Sample Problem 4 = P1V1 T1 P2V2 T2
If a gas occupies 1050 L at a P of 720 mm Hg and a T of 250 K, what V will it occupy at a P of 600 mm Hg and a T of 800 K?
P1V1 T1
P2V2 T2 =

36. ( ) ( ) Sample Problem 4 (250 K) 720 (1050 L) (800 K) (V2) 600 =
If a gas occupies 1050 L at a P of 720 mm Hg and a T of 250 K, what V will it occupy at a P of 600 mm Hg and a T of 800 K?
(250 K)
720
mm Hg ( )
(1050 L)
(800 K)
(V2)
600
mm Hg ( ) =
(720)(1050)(800) =
(250)(600)V2

37. Sample Problem 4
If a gas occupies 1050 L at a P of 720 mm Hg and a T of 250 K, what V will it occupy at a P of 600 mm Hg and a T of 800 K?
V2 = 4,032 L

38. Sample Problem 5
If a gas with V of 45 L at 700 mm Hg and 300 K changes to STP, what is its new V?
(300 K)
700
mm Hg ( )
(45 L)
(273 K)
(V2)
760
mm Hg ( ) =
(700)(45 L)(273) =
(760)(300)V2

39. Sample Problem 5
If a gas with V of 45 L at 700 mm Hg and 300 K changes to STP, what is its new V?
37.7 L = V2

40. Question
If a gas occupies 324 mL at a P of 526 torr and a T of 322 K, what V will it have at 433 torr and 221 K?
270 mL
1,037 mL
389 mL
1,024 mL

41. (433 torr)V2 = (221 K) (526 torr)(324 mL) (322 K)
37,663,704 mL = 139,426 V2
270 mL = V2

42. Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases equals the sum of the partial pressures.

43. Dalton’s Law of Partial PressuresPT = P1
+ P2
+ P3
+ …

44. = + +
Chemistry textbook, p. 255

45. the pressure exerted by the vapor emitted by a liquid or a solid
Vapor Pressure
the pressure exerted by the vapor emitted by a liquid or a solid

46. Vapor Pressure
Patm =
Pgas +
H2O P
Patm −
H2O P =
Pgas

47. Question 32 mm Hg 780 mm Hg 716 mm Hg
A gas is collected over water. The P is 748 mm Hg. The T is 30°C. What is the partial P of the gas?
32 mm Hg
780 mm Hg
716 mm Hg
Not enough information

48. Patm −
H2O P =
Pgas
748 torr – 32 torr
= 716 torr