Fall 07 HW2 solution - Homework Assignment#2 Name...

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Homework Assignment #2 Name____________________________ Laboratory Section (circle one) MW1.30 MW6.30 TTh7 1. Chapter 1, Problem 6, 23, 30, 35, 41, 56, 66 (a only), 90 1.6 Plan: Apply the definitions of chemical and physical changes to the examples. Solution: a) Not a chemical change, but a physical change — simply cooling returns the soup to its original form. b) There is a chemical change — cooling the toast will not “un-toast” the bread. c) Even though the wood is now in smaller pieces, it is still wood. There has been no change in composition, thus this is a physical change , and not a chemical change. d) This is a chemical change converting the wood (and air) into different substances with different compositions. The wood cannot be “unburned.” 1.23 Plan: Anything that increases the mass or decreases the volume will increase the density. Solution: a) Density increases . The mass of the chlorine gas is not changed, but its volume is less. b) Density remains the same . Neither the mass nor the volume of the solid has changed. c) Density decreases . Water is one of the few substances that expands on freezing. The mass is constant, but the volume increases. d) Density increases . Iron, like most materials, contracts on cooling, thus the volume decreases while the mass does not change. e) Density remains the same . The water does not alter either the mass or the volume of the diamond. 1.30 a) Plan: Use conversion factors: (0.01 m) 2 = (1 cm) 2 ; (1 km) 2 = (1000 m) 2 Solution: (17.7 cm 2 ) (0.01 m/1 cm) 2 (1 km/1000 m) 2 = 1.77 x 10 –9 km 2 b) Plan: Use conversion factor: (1 inch) 2 = (2.54 cm) 2
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