15 Energy and Chemical Change BIGIDEA Write the Big Idea for this chapter.

Transcription

1 15 Energy and Chemical Change BIGIDEA Write the Big Idea for this chapter. Chemical reactions usually absorb or release. Use the What I Know column to list the things you know about the Big Idea. Then list the questions you have about the Big Idea in the What I Want to Find Out column. As you read the chapter, fill in the What I Learned column. K What I Know W What I Want to Find Out L What I Learned 253

2 15 Energy and Chemical Change 1 Energy 2(G), 11(A), 11(B), 11(D) MAINIDEA Write the Main Idea for this lesson. Energy can change form and flow, but it is always conserved. REVIEW VOCABULARY Recall the definition of the Review Vocabulary term. temperature temperature a measure of the average kinetic of the particles in a sample of matter NEW VOCABULARY law of conservation of Chemical potential calorie joule specific Define each New Vocabulary term. law of conservation of Chemical potential law stating that in any chemical reaction or physical process, can be converted from one form to another, but it is neither created nor destroyed of its composition the ability to do work or produce the stored in a substance because that is in the process of flowing from a warmer object to a cooler object calorie j oule the amount of required to raise the temperature of one gram of pure water one degree Celsius (1ºC) SI unit for and ; one joule is equivalent to calories specific the amount of required to raise the temperature of one gram of a substance by one degree Celsius 254

3 Use with pages Compare and contrast kinetic with potential. Kinetic is the of motion. Potential is of the composition or position of an object. On the curve below that represents the skier on a ski slope on page 516, label the place of greatest kinetic A, least kinetic B, greatest potential C, and least potential D. B C A D Describe the skier above as a function of the law of conservation of. Before the skier starts, there is potential that is converted to kinetic, then to potential as the skier stops. Energy changes form. Explain chemical potential. Chemical potential of a substance is a result of the arrangement of its atoms and the strength of the chemical bonds joining the atoms. During some chemical reactions, such as burning fuel, much of the potential may be released as. Some of the may be converted to work, which is a form of kinetic. GET IT? State the law of conservation of in your own words. Energy may change forms but is never gained or lost. 255

4 Use with pages Identify each symbol in the equation for specific. q = c m ΔT q c m ΔT represents absorbed or released represents the specific of the substance represents mass of a sample in grams represents a change in temperature Summarize. Fill in the blanks to help you take notes while you read Example Problem. Problem The temperature of a sample of iron with a mass of 10.0 g changed from 50.4 C to 25.0 C with the release of 114 J. Determine the specific of iron. 1. Analyze the Problem Known: Unknown: released = 114 J specific of iron =? ΔT = 50.4 C 25.0 C = 25.4 C mass of iron = 10.0 g 2. Solve for the Unknown Write the equation for absorption. q = c m ΔT Solve for c. q = c m ΔT c = m ΔT c = q m ΔT 114 J (10.0g) (25.4 C) =0.499 J / (g. C) 3. Evaluate the Answer If the values used in the calculations have three significant figures, the answer must also have three significant figures. The calculated value matches the value for iron in Table

5 REVIEW IT! 7. MAINIDEA Explain how changes from one form to another in an exothermic reaction. In an endothermic re action. Chemical potential changes to in exothermic reactions, and the is released. In endothermic reactions, is absorbed and changed to chemical potential. 8. Distinguish between kinetic and potential in the following examples: two separated magnets; an avalanche of snow; books on library shelves; a mountain stream; a stock-car race; separation of charge in a battery. Two separated magnets illustrate potential. In a snow avalanche, positional potential changes to kinetic. Books on a shelf illustrate positional potential. As water races down a mountain stream, positional potential changes to kinetic. In a stock car race, chemical potential changes to kinetic. The separation of charge in a battery illustrates electrical potential. 9. Explain how the light and of a burning candle are related to chemical potential. Chemical poten tial, contained in the candle, is changed to in the form of light and and released as the chemical combustion reaction takes place. 10. Calculate the amount of absorbed when 5.50 g of aluminum is ed from 25.0 C to 95.0 C. The specific of aluminum is J/(g C). 345 J 11. Interpret Data Equal masses of aluminum, gold, iron, and silver were left to sit in the Sun at the same time and for the same length of time. Use Table 2 to arrange the four metals according to the increase in their temperatures from largest increase to smallest. The temperature change is inversely proportional to specific : aluminum, iron, silver, gold. 257