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Introductory Chemistry: A Foundation , Fifth Edition
Steven S. Zumdahl, University of Illinois
Media Activities
Chapter 6: Chemical Reactions: An Introduction
Understanding the concepts Check your answers Check your answers
1.a. A chemical reaction involves the change of one or more substances into other substances. What are some observations that indicate that a chemical reaction has occurred? Check your answer by opening the Some Clues That a Chemical Reaction Has Occurred Table on the Web site.
b. When a chemical reaction occurs, mass is said to be conserved. What does this mean? Why is mass conserved in a chemical reaction? When charcoal in a grill is burned, the mass of the charcoal before burning is much greater than the mass of ashes left after burning. How can this be if mass is conserved in a chemical equation?
c. Atoms are conserved in a chemical reaction (atoms are neither created nor destroyed). Are molecules conserved in a chemical reaction? Give an example to justify your answer.
d. The physical states of the reactants and products should be indicated in a chemical equation. What does aq indicate? When water is reacted or produced in a chemical reaction, is the physical state of water indicated with an aq? Explain
2.a. Open the Conservation of Mass and Balancing Equations Understanding Concepts on the CD to review important characteristics of chemical equations. Try the Exercises to test your ability to balance chemical equations. Click on the + or - buttons to determine the correct coefficients. You must choose the coefficients for the reactants first before determining the product coefficients. The best balanced equation has smallest whole number integers. However, any chemical equation can be balanced in an infinite number of ways. Explain.
b. Does the molecule ratio between two species in a chemical equation change if smallest whole number integers are not used to balance the equation? Using the Combustion of Methane Exercise, determine some combinations of coefficients other than smallest whole number integers to balance the equation. How are the coefficients related to the smallest whole number coefficients? Pick two substances and determine the molecule ratio between these substances for each possible balanced reaction. How do the molecule ratios compare?
3.a. The only way to become proficient at balancing chemical equations is to practice. For practice, do Problems 6.38 and 6.40 in the text.
3.b. Good exam questions on balancing equations involve giving the names of the compounds reacted and produced in a reaction instead of the formulas. This requires you to write correct formulas and to balance the equation. If your chemical formulas are incorrect, then there is no way you can come up with a correct balanced equation. Do Problems 6.52, 6.54, 6.56, 6.58, 6.64, and 6.66 in the text to practice these types of problems.
4. Check your understanding of important definitions in Chapter 6 by opening Key Words on the CD. Come up with your own definition before clicking on the term.
5. Test your understanding of Chapter 6 by taking the ACE quizzes on the Web site.