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General Chemistry Principles, Patterns, and Applications, 2011

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1 cal = 4.184J exactly<br />

1 J = 0.2390 cal<br />

In this text, we will use the SI units—joules (J) <strong>and</strong> kilojoules (kJ)—exclusively, except when we deal with nutritional<br />

information, addressed in Section 5.4 "Thermochemistry <strong>and</strong> Nutrition".<br />

E X A M P L E 1<br />

a. If the mass of a baseball is 149 g, what is the kinetic energy of a fastball clocked at<br />

100 mi/h?<br />

b. A batter hits a pop fly, <strong>and</strong> the baseball (with a mass of 149 g) reaches an altitude of 250<br />

ft. If we assume that the ball was 3 ft above home plate when hit by the batter, what is<br />

the increase in its potential energy?<br />

Exercise<br />

a. In a bowling alley, the distance from the foul line to the head pin is 59 ft, 10 13/16<br />

in. (18.26 m). If a 16 lb (7.3 kg) bowling ball takes 2.0 s to reach the head pin, what is its<br />

kinetic energy at impact? (Assume its speed is constant.)<br />

b. What is the potential energy of a 16 lb bowling ball held 3.0 ft above your foot?<br />

Answer:<br />

a. 3.10 × 10 2 J<br />

b. 65 J<br />

K E Y E QU A T I ON S<br />

general definition of work<br />

Equation 5.1: w = Fd<br />

Equation 5.2: w = mad<br />

relationship between energy, heat, <strong>and</strong> work<br />

Equation 5.3: ΔE = q + w<br />

kinetic energy<br />

KE= ½ mv(squared)<br />

potential energy in a gravitational field<br />

Equation 5.6: PE = mgh<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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