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Key Terms for the Unit: • matter • states of matter • solid • liquid • gas • temperature • mass • physical property • physical change • chemical property • chemical change • chemical reaction
Physical Changes
Physical Changes
I can recognize physical changes in objects or substances. (Knowledge)
I can associate physical changes with daily products. (Knowledge)
I can plan and carry out investigations of physical changes by manipulating, separating and mixing dry and liquid materials. (Skill)
I can communicate data from my investigations to provide evidence of physical changes. (Product)
Physical changes are limited to changes that result in a difference in the display without changing the composition. A physical change does not actually create a new substance with new properties, but it may create a new form (shape, etc.) of the substance. Items can be mixed and separated without altering their chemical makeup. A physical change represents a change in state as opposed to a change in matter. Some common changes (but not limited to) are:
Texture
Color
Temperature
Shape (cutting)
Change of State (Boiling Point and Melting Point are significant factors in determining this change.)
Physical properties include many other aspects of a substance. The following are (but not limited to) physical properties.
Luster
Malleability
Ability to be drawn into a thin wire
Density
Viscosity
Solubility
Mass
Volume
States of Water
States of Water
I can recognize states of water. (Knowledge)
I can explain the how temperature changes impact particle movement in states of water. (Reasoning)
I can construct an argument about the physical changes in water due to temperature changes. (Product)
Matter normally exists as either a solid, a liquid, or a gas. We call this property of matter the phase of the matter. The three normal phases of matter have unique characteristics. The addition or removal of heat / energy causes water to change state. The changing states of water are directly linked to the addition or removal of heat.
Solid - In the solid phase the molecules are closely bound to one another by molecular forces. A solid holds its shape and the volume of a solid is fixed by the shape of the solid. The particles move the slowest in a solid due to the temperature being the lowest.
Liquid - In the liquid phase the molecular forces are weaker than in a solid. A liquid will take the shape of its container with a free surface in a gravitational field. In microgravity, a liquid forms a ball inside a free surface. Regardless of gravity, a liquid has a fixed volume.
Gas - In the gas phase the molecular forces are very weak. A gas fills its container, taking both the shape and the volume of the container.
Plasm - The resulting mixture of neutral atoms, free electrons, and charged ions is called a plasma. A plasma has some unique qualities that causes scientists to label it a "fourth phase" of matter. A plasma is a fluid, like a liquid or gas, but because of the charged particles present in a plasma, it responds to and generates electro-magnetic forces.
Freezing
Freezing
Freezing is the change that occurs when a liquid changes into a solid as the temperature decreases.
Substances freeze at exactly the same temperature as they melt. As a consequence, the temperature at which—under a specified pressure—liquid and solid exist in equilibrium is defined as the melting or freezing point. When the pressure is one atmosphere, this temperature is known as the normal freezing (or melting) point. A change in pressure will change the temperature at which the change in the state of matter occurs. A decrease in pressure will decrease the temperature at which this occurs and an increase in pressure will increase the temperature required.
Evaporation
Evaporation
Evaporation is the process by which water changes from a liquid to a gas or vapor. Steam is an indication that evaporation has occurred. Evaporation is the primary pathway that water moves from the liquid state back into the water cycle as atmospheric water vapor. Studies have shown that the oceans, seas, lakes, and rivers provide nearly 90 percent of the moisture in the atmosphere via evaporation, with the remaining 10 percent being contributed by plant transpiration.
Condensation
Condensation
Condensation is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds. These clouds may produce precipitation, which is the primary route for water to return to the Earth's surface within the water cycle. Condensation is the opposite of evaporation.
Melting
Melting
When a solid turns into a liquid it is called melting. There is a temperature at which this happens called the melting point. As the energy in the molecules increases from a rise in temperature, the molecules start moving faster. Soon they have enough energy to break free of their rigid structure and start moving around more easily. The matter becomes a liquid. The melting point for water is 0 degrees C (32 degrees F). When the opposite happens and a liquid turns into a solid, it is called freezing.
Chemical Changes
Chemical Changes
I can recognize evidence that can be used to support a claim that a chemical change occurred to a substance. (Knowledge)
I can identify investigations that can be used to determine if a chemical change occurred based on observable evidence. (Knowledge)
I can differentiate between physical and chemical changes. (Reasoning)
I can cite and explain examples illustrating physical or chemical changes. (Reasoning)
I can plan and carry out an investigation to determine if a chemical change occurred based on observable evidence. (Skill)
I can communicate data from my investigations to provide evidence of chemical changes. (Product)
Chemical change results in the transformation of one molecular substance into another, the creation of a new substance. Gasoline burns, reacting with oxygen in the atmosphere, generating light, heat, and converting the carbon-based molecules into carbon dioxide gas and water vapor. When substances combine like this and undergo chemical changes, we say that a chemical reaction has occurred. Some chemical reactions are quite evident, like the burning of gasoline, and involve the production of heat or light. In other types of chemical reactions, gases are evolved, color changes occur and clear solutions become cloudy, with the ultimate formation of an insoluble substance (a precipitate). Chemical changes can also be quite obscure and their occurrence can only be detected by sophisticated chemical analysis.
change in color
change in temperature
noticeable odor
formation of a solid precipitate (precipitation)
formation of bubbles or foam
production of gas
rusting
burning
applying heat - cooking
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