Data Analysis
Why Was Mercury Used in Thermometers?
Until recently, mercury thermometers were used in homes and schools. When a thermometer broke, people were exposed to mercury. When broken thermometers were thrown away, they ended up in landfills. Mercury is a toxic substance that can harm humans and other organisms. Schools no longer use mercury thermometers and people are encouraged to replace their fever thermometers.
So why did people continue to use mercury thermometers long after they knew the dangers of mercury? Look at the data table. It lists some densities over a temperature range from 0°C to150°C. The temperatures are given at 30-degree intervals.
Using Tables How does the density of mercury change as the temperature increases?
Relating Cause and Effect How does a change in density affect the volume of a mercury sample?
Density of Mercury
Temperature (°C)
Density (g/mL)
Volume of One Gram (mL)
0
13.60
0.07356
30
13.52
0.07396
60
13.45
0.07436
90
13.38
0.07476
120
13.30
0.07517
150
13.23
0.07558
Calculating If a thermometer contained a gram of mercury, how much would the volume of the mercury change when the temperature rose from 0°C to 30°C? From 30°C to 60°C? From 60°C to 90°C? From 90°C to 120°C?
Drawing Conclusions Why was mercury a better choice than water for the liquid in a thermometer? (Hint: Between 0°C and 30°C, the volume of a gram of water changes by 0.0042 mL. Between 30°C and 60°C, the volume changes by 0.0127 mL. Between 60°C and 90°C, the volume changes by 0.0188 mL.)
Inferring Why is the mercury in a thermometer stored in a narrow tube?
Kinetic Theory
Why, under ordinary conditions, is copper a solid, mercury a liquid, and helium a gas? To begin to answer that question, you need to know something about kinetic energy. An object that is moving has kinetic energy. The word kinetic comes from a Greek word meaning “to move.” Kinetic energy is the energy an object has due to its motion.
The faster an object moves, the greater its kinetic energy is. A ball thrown at 85 miles (137 kilometers) per hour by the pitcher in Figure 5 has more kinetic energy than a ball thrown at 78 miles (125 kilometers) per hour. When a baseball is thrown, a batter can see that it is moving. But the batter cannot see that there is also motion occurring within the baseball. According to the kinetic theory of matter, particles inside the solid baseball are moving. Particles in the air that the baseball travels through are moving too.
The kinetic theory of matter says that all particles of matter are in constant motion. The theory was developed in the mid-1800s to explain the behavior of gases. It can also help to explain the behavior of liquids and solids.
Figure 5 The kinetic energy of a baseball depends on the speed at which the pitcher throws the ball.
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