Thursday, 8 August 2013

మన చుట్టూ ఉండే పదార్థం (9 వ తరగతి ) :: QUIZ ON LIQUIDS & GASES


1: All materials move from solid to liquid to gas as the temperature increases.
a. True
b. False*
Explanation: Not all materials move through all three phases as temperatures increase. Some materials, including carbon dioxide (CO2), can move directly from solid to the gaseous state of matter. The term used to describe this change of state is "sublimation." You can see it happen whenever you watch dry ice evaporate.

2: What term is used to describe the phase change of a solid to a liquid?
a. Freezing
b. Melting*
c. Boiling
d. None of the Above
Explanation: Melting is the process of a solid becoming a liquid. The melting point is the temperature that a compound will move from the solid to liquid state. Ice (H2O) melts at 0 degrees Celsius. Other compounds shift from solid to liquid states at other temperatures. The melting point for pure potassium (K) is 64 degrees Celsius.

3: What phase of matter would you expect to find this compound at room temperature? :: H2O
a. Solid
b. Liquid*
c. Gas
d. Plasma
Explanation: H20 is the formula for the compound known as water. We suppose it becomes easy after that. Is water a solid, liquid, or a gas at room temperature? It's a liquid. Below 0 degrees Celsius, water is a solid. It's a gas above 100 degrees Celsius.

4: Forces of attraction in liquids are ___ than in solids.
a. Weaker*
b. Stronger
c. About the Same
Explanation: Forces of attraction in liquids are weaker than the forces of attraction in solids. It might be a complicated term, but it's an easy concept. Think about a block of ice (H2O). Try to pull it apart with your hands. The only way to break it apart is to crack it. That effort requires a lot of energy. Now think about a glass of water. Try putting your hand in a bowl of water and take some water out. Hey! That's pretty easy. It's easy because the forces of attraction are weaker in the liquid form.

5: It is just as easy to compress a liquid, as it is to compress a gas.
a. True
b. False*
Explanation: It is much harder to compress the molecules of a liquid than the molecules of a gas. It is harder to compress a liquid because the molecules are already very close together. A gas has molecules that are spread out and it's easier to push them together. Engineers use this concept when they make items such as shock absorbers for your car. They inject gas into cylinders. As your car hits bumps in the road, the cylinders compress the gas and it absorbs some of the energy. You couldn't make the same type of shock absorbers with liquids or solids because the molecules are already so close together.

6: All liquids have same...
a. Density
b. Viscosity
c. Solubility
d. None of the Above*
Explanation: That's right, we tried to trick you. All compounds in a liquid state have different physical properties. Liquids have different densities. That means their molecules are closer together or further apart. Viscosity, or the ability to flow, is also different. Water (H2O) has a lower viscosity than tree sap. Solubility is the ability that one substance can be dissolved in another. Table salt (NaCl) may be easily dissolved in water, but not as easily in oil. All liquids, just like all compounds, are a little bit different.

7: Liquids that move quickly downhill are described as having...
a. High Viscosity
b. Low Viscosity*
c. Heavier
Explanation: Viscosity is a measure at how well fluids flow. You can think of it as friction inside the liquids. If there is a lot of friction, the fluid will move slower downhill. With less friction, lower viscosity, the fluid can move quickly downhill. Examples of liquids with low viscosity are water (H2O) and alcohol (C2H6O). Highly viscous liquids include tree sap and oil.

 8: All liquids can be combined to form solutions.
a. True
b. False
Explanation: Not all liquids can be combined to form solutions. Liquids may be combined to form heterogeneous mixtures. To have a solution, the mixture must be homogeneous. If you tried to combine mercury (Hg) and water (H2O), you would have a mixture, but not a solution. The two liquids will not evenly mix because of the different densities. Heavy mercury will just sit at the bottom of the container. In this case, it has something to do with solubility.

9: No pure elements are liquids at room temperature.
a. True
b. False*
Explanation: While most of the elements you think of are either gas or solid at room temperature, there are a few exceptions. Mercury (Hg) is the easy answer. You may have seen it in your classes or in your thermometers. It is always liquid at room temperature. A little less common is the element bromine (Br). These two elements are rare exceptions on the periodic table. There are many elements that melt at temperatures just a little warmer than room temperature. Cesium (Cs), rubidium (Rb), and gallium (Ga) are examples of those elements.

10: Evaporation and boiling are the same process because molecules move from a liquid to gas state.
a. True
b. False*
Explanation: Evaporation and boiling are much different processes. The process of boiling occurs when the temperature of the entire system reaches a special point. At that point, the energy of the system increases and liquid molecules gain the energy to become a gas. The energy is spread throughout the entire system.

Evaporation is a process that happens on a molecular level. In any system, molecules have different amounts of energy. Some molecules have very little while others are super-excited. Evaporation can happen when the average temperature of a system is much lower than the boiling point and some super-excited molecules zip away from the system and become a gas. The key difference in the two processes is the fact evaporation happens on a molecular level at temperatures far below the boiling point


1: As the temperature of a system increases, the pressure of the gases.
a. Increases*
b. Decreases
c. Stays the Same
Explanation: As the temperature of a system increases, the pressure of the gases in that system increases. It makes sense to think of it as adding energy to molecules. As you add energy/heat, the gas molecules bounce around more and the pressure goes up. This idea is also known as the Gay-Lussac's Law.

2: What is the term used to describe the phase change of a liquid to a gas?
a. Boiling*
b. Condensation
c. Melting
d. None of the Above
Explanation: Boling is the process of liquid molecules changing to the gas state. The boiling point is the temperature at which the molecules of a liquid gain enough energy to become a gas. The boiling point of water (H2O) is 100 degrees Celsius. When water reaches that temperature, the molecules gain the energy to become steam and escape the water.

3: Gas molecules are always evenly distributed in the atmosphere.
a. True
b. False*
Explanation: Many localized areas on the surface of the Earth have gases at different concentrations. Scientists have discovered areas near volcanoes that contain high concentrations of carbon dioxide (CO2) gas than can kill any living things (even trees). The carbon dioxide collects near the surface because it is heavier than the gases that make up most of the atmosphere.

4: As the volume of a specific amount of gas decreases, it's pressure...
a. Increases*
b. Decreases
c. Stays the Same
Explanation: If you have "X" amount of gas and you decrease the size of the container, the pressure of the gas will increase. A good real example of this increased pressure is found in SCUBA tanks. Special equipment will compress the amount of air that may be used to fill a room so that it fits in a small air tank. The pressure in the tank is very high when compared to the normal pressure found in the room. The concept that pressure increases as the volume decreases is also called Boyle's Law.

5: Which of these statements is true?
a. Gases have high density.
b. Gases can be compressed more than solids.*
c. Gases have very specific shapes.
d. All of the Above
Explanation: There is only one true statement of the three choices. Gases can be compressed more than solids. Gases have their molecules spread out so it is easier to push them all together. Solids have their molecules very close together and are denser. As far as the other choices... Gases have a much lower density than both liquids and solids. Gases are also known for not having shapes of any kind. They usually fill up the container, no matter what shape that might be.

6: As the temperature of a gas decreases, its volume...
a. Increases
b. Decreases*
c. Stays the Same
Explanation: As the temperature of a gas decreases, its volume tends to decrease as well. Generally, the molecules of a gas have a lot of energy and are very active. As the temperature of a system goes down, energy is removed from those molecules and they become less active. When the molecules lose energy, they don't bounce around as much and stay closer together. When the space between the molecules decreases, that means the volume used by the gas decreases. This process is also called Charles's Law.

7: The molecules in a gas are in constant motion.
a. True*
b. False
Explanation: The molecules in a gas are in constant motion. Actually, all molecules in solids, liquids, and gases are in constant motion at any temperature above absolute zero. The molecules in a gas are just more active than the molecules found in solids and liquids.

8: Gases at higher temperatures generally have...
a. More energy than at cooler temperatures.*
b. Less energy than gases at cooler temperatures.
c. Are defined as plasmas.
Explanation: As the temperature of a gas increases, it has more energy. That energy makes the gas more active and can also increase factors like pressure and volume. It takes more than an increase in temperature to create a plasma. Plasmas are groups of molecules that have had their electrons stripped away. Hot gases are sometimes just super hot.

9: Which of these choices is defined as "Standard Pressure?"
a. 14.7 psi
b. 1 atm
c. 760 torr
d. All of the Above*
Explanation: All of the choices are different ways of explaining standard pressure. "psi" is an acronym that stands for "Pounds per square inch." An "atm" is one atmosphere of pressure. "Torr" is a measure of millimeters of mercury in a barometer. So what is standard pressure? It's the atmospheric pressure at sea level.

10: Gases have the same pressure throughout the entire atmosphere.
a. True
b False*
Explanation: The atmosphere is actually thicker near the surface of the Earth. The pressure decreases as your altitude increases. You can understand this fact if you measure the weight of air at sea level (standard pressure). At sea level, the pressure of the air is 14.7 pounds per square inch. That definition means that there is a column of air, one inch square, which reaches to the top of the atmosphere. That column of air weighs 14.7 pounds. As you go higher in the atmosphere, there is less air above you... So the force pushing on you decreases.

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