Cracking the AP Chemistry Exam 2020, Premium Edition by The Princeton Review

Author:The Princeton Review
Language: eng
Format: epub
Publisher: Random House Children's Books
Published: 2019-10-21T16:00:00+00:00

Chapter 7

Big Idea #5: Laws of Thermodynamics and Changes in Matter

The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.

HEAT AND TEMPERATURE

Many people do not understand that heat and temperature are not, in fact, synonyms. The fact is, while the concepts are certainly related, they represent different things. Temperature represents the average amount of kinetic energy present in a given substance. Heat represents energy flow between two substances at different temperatures. Energy can be neither created nor destroyed; the amount of energy in the universe is constant. This is sometimes called the First Law of Thermodynamics.

Energy transfers due to molecular collisions. As the faster-moving molecules collide with the slower-moving ones, they transfer some of their energy, changing the speed of both molecules. We’ve already defined the terms exothermic and endothermic in terms of enthalpy back in Chapter 5, but those terms can also be defined another way when studying the energy flow that takes place with many physical and chemical processes. In an exothermic process, energy is transferred from the reaction itself to its surroundings. If you dissolve salt in water and the temperature of the water increases, it is because the process itself (the salt dissolving in water) emitted energy. The surroundings (in this case, the water), absorbed it.

For an endothermic process, the opposite is true. Energy transfers from the surroundings into the process. When an ice cube melts in your hand, the energy leaves your hand (and the surrounding air) and goes into the ice cube. This is an endothermic process. Both physical and chemical changes can be classified as exothermic or endothermic.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.