11 4 temperature and volume 4th ed

Chapter 11 Lecture

Basic Chemistry Fourth Edition

Unit 3 Gases Temperature and Volume (Charles’s Law) Learning Goal Use the temperature–volume relationship (Charles’s law) to determine the final temperature or volume when the pressure and amount of gas are constant. © 2014 Pearson Education, Inc.

Charles’s Law Charles’s law states that • the temperature (K) of a gas is directly related to its volume (V) when P and n are constant • if the temperature (K) increases, then the volume (V) also increases

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Figure 11.5 Charles’s law: The Kelvin temperature of a gas is directly related to the volume of the gas when there is no change in the pressure and amount of gas. When the temperature increases, making the molecules move faster, the volume must increase to maintain constant pressure.

Charles’s Law Charles’s law is a direct relationship between volume and temperature. A direct relationship between variables means the variables increase or decrease together. No change in number of moles and pressure All temperatures used in gas law calculations must be converted to Kelvin (K) temperature. © 2014 Pearson Education, Inc.

Charles’s Law Equation The equation for Charles’s law can be rearranged to solve for any factor.

To obtain V2, multiply both sides by T2.

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Learning Check Use the gas laws to complete the following statements with increases or decreases. A. Temperature _______ when V decreases. B. When T decreases, V _______. C. Pressure _______ when V changes from 12 L to 4 L. D. Volume _______ when T changes from 15 oC to 45 oC.

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Solution Use the gas laws to complete the following statements with increases or decreases. A. Temperature decreases when V decreases. B. When T decreases, V decreases. C. Temperature decreases when V changes from 12 L to 4 L. D. Volume increases when T changes from 15 oC to 45 oC.

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Learning Check Solve Charles’s law expression for T2.

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Solution Solve Charles’s law expression for T2.

Cross multiply to give: V1T2 = V2T1 Solve for T2 by dividing through by V1

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Learning Check A balloon has a volume of 785 mL at 21 oC. If the temperature drops to 0 oC, what is the new volume of the balloon (n, P constant)?

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Learning Check A balloon has a volume of 785 mL at 21 oC. If the temperature drops to 0 oC, what is the new volume of the balloon (n, P constant)? Step 1 Organize the data in a table of initial and final conditions. We can predict that as T decreases, V decreases. Conditions 1

Conditions 2

V1 = 785 mL

V2 = ?

T1 = 21 °C = 294 K

T2 = 0 °C = 273 K

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Solution A balloon has a volume of 785 mL at 21 oC. If the temperature drops to 0 oC, what is the new volume of the balloon (n, P constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity. Solve Charles’s law for V2. Decreasing temperature decreases the volume when moles and pressure are constant.

© 2014 Pearson Education, Inc.

Solution A balloon has a volume of 785 mL at 21 oC. If the temperature drops to 0 oC, what is the new volume of the balloon (n, P constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity.

© 2014 Pearson Education, Inc.

Solution A balloon has a volume of 785 mL at 21 oC. If the temperature drops to 0 oC, what is the new volume of the balloon (n, P constant)? Step 3 Substitute values into the gas law equation and calculate. When temperature decreases, the volume decreases as predicted.

© 2014 Pearson Education, Inc.