Now answer these questions What are solids, liquids and gases made out of? Are the particles moving or still? Do the gas particles move more or less than in a liquid? Do the gas particles move more or less than in a solid? A change from a solid to a liquid is called what? A change from a liquid to a gas is called what? A change from a gas to a liquid is called what?
A change from a liquid to a solid is calles what? If liquid particles are heated do they move more or less? If you give heat energy to a liquid will it change into a gas or a solid? What is the name of the process when a liquid changes into a gas? This is known as reaching a state of thermal equilibrium. Matter is all around you. It is everything in the universe — anything that has both mass and volume and takes up space is matter.
Matter exists in different physical forms — solids, liquids and gases. All matter is made of tiny particles called atoms, molecules and ions. These tiny particles are always in motion — either bumping into each other or vibrating back and forth. It is the motion of particles that creates a form of energy called heat or thermal energy that is present in all matter.
The particles in solids are tightly packed and can only vibrate. The particles in liquids also vibrate but are able to move around by rolling over each other and sliding around. In gases, the particles move freely with rapid, random motion. At higher temperatures, particles have more energy.
Some of this energy can be transmitted to other particles that are at a lower temperature. For example, in the gas state, when a fast moving particle collides with a slower moving particle, it transfers some of its energy to the slower moving particle, increasing the speed of that particle.
With billions of moving particles colliding into each other, an area of high energy will slowly transfer across the material until thermal equilibrium is reached the temperature is the same across the material. If heated sufficiently, the movement of particles in a solid increases and overcomes the bonds that hold the particles together.
The substance changes its state from a solid to a liquid melting. If the movement of the particles increases further in the liquid, then a stage is reached where the substance changes into a gas evaporation. Convection transfers heat energy through gases and liquids. As air is heated, the particles gain heat energy allowing them to move faster and further apart, carrying the heat energy with them.
Warm air is less dense than cold air and will rise. Removing heat from a substance changes a gas to a liquid or a liquid to a solid. Two key points are worth emphasizing.
Take water H 2 O as an example. However, if heat is added, some of the solid H 2 O will melt and turn into liquid H 2 O. If heat is removed, the opposite happens: some of the liquid H 2 O turns into solid H 2 O. Water is a good substance to use as an example because many people are already familiar with it. Other substances have melting points and boiling points as well. Again, consider H 2 O as an example. Only after all of the solid has melted into liquid does the addition of heat change the temperature of the substance.
For each phase change of a substance, there is a characteristic quantity of heat needed to perform the phase change per gram or per mole of material. Remember that a phase change depends on the direction of the heat transfer. If heat transfers in, solids become liquids, and liquids become solids at the melting and boiling points, respectively.
If heat transfers out, liquids solidify, and gases condense into liquids. At these points, there are no changes in temperature as reflected in the above equations. How much heat is necessary to melt The heat of fusion of H 2 O is Note the units on these quantities; when you use these values in problem solving, make sure that the other variables in your calculation are expressed in units consistent with the units in the specific heats or the heats of fusion and vaporization.
This phase change is called sublimation. Each substance has a characteristic heat of sublimation associated with this process. We encounter sublimation in several ways. You may already be familiar with dry ice, which is simply solid carbon dioxide CO 2.
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