Lesson 2 Changes in Temperature PDF

LESSON 2 Classification and States of Matter Changes in Temperature Essential Question What happens to a frozen lake when the What do you think? Read the two...

LESSON 2 Classification and States of Matter Changes in Temperature Essential Question What happens to a frozen lake when the What do you think? Read the two statements below and decide temperature changes? whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After  hermal energy moves from cooler objects to T warmer objects. A change in temperature can change the volume of a gas. Study Coach What happens to the volume of a gas Make an outline as you read to summarize the when thermal energy changes? information in the lesson. Recall that adding energy to a substance increases the kinetic Use the main headings in energy of the particles. Adding energy can also affect the the lesson as the main volume of a substance. headings in your outline. Use your outline to review Jacque Charles (1746–1823) was a French scientist who the lesson. described the relationship between temperature and volume of a gas. Charles was interested in balloons. Because of this, Charles had practical experience with the behavior of gases. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use Volume-Temperature Law Charles’s law states that the volume of a gas increases with increasing temperature, if the pressure is constant. You have probably seen Charles’s law in action if you have ever taken a balloon outside on a cold winter day. When the balloon is in cold air, the temperature of the gas inside the balloon decreases. Recall that a decrease in temperature is a decrease in the average kinetic energy of particles. As a result, the gas particles slow down. They begin to get closer together. Fewer particles hit the inside of the balloon. The balloon seems to be only partway filled. Thermal contraction is a decrease in a volume as its temperature decreases. 8 Classification and States of Matter Reading Essentials  If the balloon is returned to a warm place, the kinetic energy of the particles increases. There are more collisions between the particles and the inside of the balloon. The collisions push outward on the balloon. The volume of the gas increases. An increase in a volume as the temperature increases is called thermal expansion. The number of particles in the balloon does not change. The object the particles are in changes size as the thermal energy changes. This happens because the space between the particles changes. The particles themselves do not change size. The volume the particles take up changes. How does thermal energy transfer between objects? Thermal energy can be added to substances. Thermal energy can be removed from substances. How do substances gain and lose thermal energy? Heating Think about holding a warm cup of cocoa on a cold day. Thermal energy moves from the warm cup to your hands. The transfer of thermal energy from a region of higher temperature to a region of lower temperature is called heat. Recall that temperature and thermal energy are not the same thing. Neither are heat and thermal energy. However, something is heated when thermal energy transfers from one object to another. How can you heat a material? You can heat a material by placing it in contact with a material that has a higher temperature. The material with the higher temperature can be a solid, liquid, or gas. Systems The materials involved in a transfer of energy are part of a system. When you hold a cup of hot cocoa, your hands, the cup, the cocoa, and the air are parts of the system. This is an example of an open system. In an open system, energy is Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use released into the environment. Scientists who study energy transfer use the idea of a closed system. In a closed system no matter or energy moves between the system and the environment. Closed systems do not actually happen in the real world, but they can be used to study energy transfer. How can air hold up water? Imagine bringing a beach ball to the beach. You use a pump to blow up the ball. The beach ball fills up, and then it pops! How does that happen? Now, think about what would happen if you placed an index card over the opening of a cup that is half- full of water and turn the cup upside down. Could the air under the index card hold the water inside the cup? Reading Essentials Classification and States of Matter 9  Particle Collisions Particles in gases are always moving. As a result of this movement, gas particles are always bumping into other particles and into their container. When particles collide with their container, pressure results. Pressure is the amount of force per unit of area applied to an object’s surface. This also explains why when you place a finger over a straw full of liquid, the liquid stays in the straw rather than falling into the glass. Your finger on the straw reduces air pressure on top of the liquid. When the straw is pulled out of the glass, there is more air pressure on the bottom than on the top. Once the finger is removed, there is equal air pressure at the top and bottom of the straw. The liquid falls out of the straw. Think back to the beach ball. When you pump air into a beach ball, the air applies a force that keeps the ball firm. Units of Pressure The pressure of gases is measured by the number of collisions of particles with the container. The higher the pressure, the more times particles collide with the container. The lower the pressure, the fewer the collisions. One way to describe pressure is by relating the pressure of the substance to the pressure that exists due to the atmosphere. Sometimes scientists use the unit atmospheres (atm). The pressure at sea level is 1 atm. A pressure of 4 atm is four times the pressure at sea level. How does pressure change when temperature changes? Temperature can affect the pressure of a substance. When conditions cause the pressure of a substance to change, containers must be strong enough to hold the pressure. If the container is not strong enough, it could pop like a burst beach ball. A flexible container can appear to be crushed if the Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use pressure inside decreases. Temperature and Pressure Changing the temperature of a gas affects its behavior. A decrease in temperature decreases the pressure of a gas. This happens because the speed of the particles decreases, and the particles collide with the container less often. Air Pressure When the thermal energy of a gas increases, the motion of the particles speeds up. As the particles move faster, they collide with their container more often. The pressure inside the container increases. 10 Classification and States of Matter Reading Essentials  What happens to states of matter as temperature changes? When seasons change, you might see ice and snow melt away. Water is one of the few substances that you frequently observe in three states of matter (solid, liquid, and gas) at Earth’s temperatures. Phase Change Ice melts when the temperature increases. What happens to the particles in ice to cause a change in state? Melting Matter can change state when it gains or loses enough thermal energy. Recall that particles speed up when their temperature increases. When the particles speed up, they move further away from each other. As they gain more and more thermal energy, they break away from the other particles, as shown below. This is the melting point of the substance. As energy is added, As particles move farther apart, Once all particles are in a liquid state, solid particles vibrate faster the solids becomes a liquid. any additional energy increases the speed and temperature increases. Temperature remains constant on the particles. Temperature increases. at the melting point. What happens when a solid reaches its melting point? The Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use temperature stops rising when it reaches the melting point of RE_P312_204A_NGMSS-BANK the matter, as shown in the figure above. Additional thermal energy causes the particles to overcome their attractive forces. The particles move farther apart and potential energy increases. Once a solid completely melts, the addition of thermal energy will cause the kinetic energy of the particles to increase again, and the temperature will start to increase. Vaporization When you heat water, do you ever notice how bubbles begin to form at the bottom and rise to the surface? The bubbles contain water vapor, a gas. As the water heats, it changes from the liquid state to the gaseous state. The change in state of a liquid into a gas is vaporization. Reading Essentials Classification and States of Matter 11  Vaporization that occurs within a liquid is called boiling. During boiling, vaporization takes place throughout the liquid. The temperature at which boiling occurs in a liquid is called its boiling point. The kinetic energy of particles increases until the liquid reaches its boiling point. At the boiling point, the potential energy of particles begins increasing. The particles move farther apart until attractive forces no longer hold them together. At this point, the liquid changes to a gas. The temperature stays at the boiling point until all of the particles have changed from liquid to gas. Evaporation You may have seen a puddle disappear, or evaporate, slowly on a sunny day. Unlike boiling, evaporation is vaporization that occurs only at the surface of a liquid, as shown in the figure. A small amount of liquid in an open container will seem to disappear after several days due to evaporation. Pressure and Evaporation Pressure also plays a role in evaporation. When a substance evaporates, the particles must overcome the force of air pressure. Air pressure is always pressing down on the liquid’s surface. For a particle to evaporate it must overcome the force of air pressure. Air pressure Evaporation Freezing Freezing is a process that is the opposite of melting— liquid changes to solid. The temperature at which matter Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use changes from the liquid state to the solid state is its freezing RE_P310_203A_NGMSS-BANK_D point. The freezing point of a substance is the same as its melting point. Freezing requires the removal of thermal energy. As energy is removed, the particles slow down. They start to form an organized structure. As a liquid becomes a solid, the temperature remains the same until all of the liquid becomes a solid. Then the temperature will start to decrease again. Condensation When a gas loses enough thermal energy, the gas changes to a liquid, or condenses. The change of state from a gas to a liquid is called condensation. Water continually changes phase on Earth’s surface. The Sun transfers energy to Earth. That energy powers the processes that cycle water through Earth’s systems. 12 Classification and States of Matter Reading Essentials