chapter 3 flash cards
A student examines a thermometer placed in a can containing a substance that is being heated. The temperature remains the same for several minutes, and then it starts to rise. Without looking in the can, how does the student know what is occurring in the can?
Because energy is being added but no increase in temperature occurs, a phase change is occurring in the can.
Unpopped popcorn kernels contain a small amount of water. Use what you know about vaporization and how gases behave to explain why popcorn pops when it is heated.
Heating causes the water to vaporize. With continued heating, the pressure of the vapor increases because the volume of the confined vapor is constant. Eventually, the increased pressure causes the kernel to burst open.
What three assumptions about particles in a gas are made by the kinetic theory?
The particles are in constant, random motion. The motion of one particle is unaffected by the motion of other particles unless the particles collide. Under ordinary conditions, forces of attraction between particles can be ignored.
What happens to the speed of the particles inside an air-filled balloon if the temperature of the balloon increases?
The particles in the air move faster, on average, when the temperature increases because they have more kinetic energy.
In a car engine, air and gasoline vapors are mixed in a cylinder. A piston is pushed into the cylinder before a spark ignites the mixture of gases. When the piston is pushed into the cylinder, what happens to the pressure of the gases in the cylinder?
The pressure increases
Compare the vapor pressure of water at 10°C with its vapor pressure at 50°C.
The vapor pressure of water is greater at 50C than 10.
If a piston moves downward in a cylinder, what happens to the volume and pressure of the gas in the cylinder? The temperature remains constant.
The volume decreases and the pressure increases.
How are the pressure and volume of a gas related?
The volume of a gas is inversely proportional to its pressure.
The SI unit of pressure is the
pascal
Provide an example of each of the three states of matter that exist at room temperature.
solid copper, liquid water, and the helium inside of a balloon as a gas.
Which of these phase changes does NOT involve changing a liquid into a gas?
sublimation
which statement is true about the the atoms in helium gas?
they are not closely packed
Boyle's law relates pressure and
volume
Increasing which variable would decrease the pressure of a contained gas?
volume
which state of matter has a definite volume but a variable shape?
liquid
in which state(s) of matter can materials take the shape of their containers?
liquids and gas
Compare and contrast liquid water and ice in terms of how definite their shapes and volumes are.
12. Both liquid water and ice have a definite volume. Ice has a definite shape, but liquid water does not.
If you take a helium balloon from inside a warm house to outside on a snowy day, what will happen to the balloon? Could you classify this change as a phase change? Explain your answer.
A balloon that is flexible will shrink. This observed change is not a phase change because helium is a gas before and after the change.
In Earth's atmosphere, pressure and temperature both decrease as altitude increases. Weather balloons expand as they rise. Which has more effect on the weather balloon, the decrease in pressure or the decrease in temperature? Explain your answer.
A decrease in pressure causes an increase in volume. A decrease in temperature causes a decrease in volume. Because the volume of the balloon increases, the decrease in pressure must affect the balloon more than the decrease in temperature.
How does an endothermic phase change differ from an exothermic phase change?
During an endothermic phase change, energy is absorbed by the system. During an exothermic phase change, energy is released by the system.
Using the kinetic theory, explain what causes gas pressure.
Gas pressure is caused by collisions of atoms with their containers.
What three factors affect the pressure of a gas in a closed container?
Temperature, volume, and the number of particles
How do the way that atoms are arranged in liquid mercury and solid copper affect the movement of mercury and copper atoms?
The atoms in copper vibrate around fixed positions. The atoms in mercury can flow past one another.
Using the kinetic theory, explain why a liquid has a definite volume but a gas does not.
The attractions between the particles in a liquid are strong enough to keep the particles close together. Without any significant attractions between particles in a gas, the particles are free to expand into any volume that is available.
If there is a gas leak in the basement of a building, you will soon notice an odor throughout the house. However, if there is a water leak in the basement, wou will need to go to the basement to detect the leak. Use the kinetic theory to explain the differences.
There is almost no attraction between particles in a gas. They will quickly spread throughout the building. Because particles in a liquid strongly attract one another, they remain close thogether and don't spread throughout the building (unless the water quantity is large and there is no drain.)
Explain why water has a different boiling point at an elevation of 3000 meters than it does at sea level.
Water boils when its vapor pressure becomes equal to atmospheric pressure. At 3000 m, the atmospheric pressure is lower than it is at sea level. Thus, vapor pressure equals atmospheric pressure at a lower temperature, and water boils at a lower temperature.
Using the kinetic theory, explain why the pressure of a gas increases when its temperature increases.
When the temperature of a gas increases, the particles have greater kinetic energy, on average, and move faster. Thus, atoms hit the walls of the container more often and with greater force, causing the pressure to increase.
Compare the melting and freezing of water in terms of (a) the temperature at which these processes take place and (b) how energy is involved in these processes
a. Water melts and freezes at the same temperature. b. Melting is an endothermic process. Freezing is an exothermic process.
The phase change that is the reverse of vaporization is
condensation
Which of the following changes is exothermic?
freezing
Which graph represents what happens to the pressure in a tire as air is added to the tire? Assume the temperature of the gas is constant.
graph a
Which graph represents what happens to the pressure in an aerosol can if the can is heated?
graph a
Which graph represents temperature versus time during a phase change?
graph c
If the speed of an object increases, its kinetic energy
increase
