Physical and Chemical Changes
SC.5.P.9.1: Investigate and describe that many physical and chemical changes are affected by temperature.
Physical and chemical changes in grades k-5 focus on how those changes are affected by temperature. Physical changes, such as the change in state of water from solid to liquid to gas and back and forth between each state are caused by adding or removing heat. Chemical changes are not related to identifying chemical changes, but rather to how chemical changes are also affected by temperature. Because identification of chemical changes is not an elementary benchmark, investigation of such popular chemical changes as baking soda and vinegar or elephant’s toothpaste are best used as engagement pieces, rather than the instructional focus. Chemical changes such as cooking and burning are caused by increases in temperature. In the case of burning, the change is both caused by heat and the source of heat,
Target 1: Observe physical changes such as changes in state, and chemical changes, such as cooking, burning, rusting, and decaying.
Water’s Change in States: Evaporating and Boiling
Water is the only substance on Earth that exists in all three states: solid, liquid, and gas. We find water vapor (gas) in the air around us. We find liquid water in the rain, rivers, lakes, and oceans all over the Earth. When it is cold enough, we will find water in a solid state (ice). Today we are going to investigate how adding and removing heat affects the changes that water goes through as it changes state.
Recognize: List the three states of matter for water and an example of each:
Room temperature is around 74 degrees Fahrenheit. When a container is filled with water and left to sit overnight, the temperature of the water will be the same as the room: it will be room temperature water. In fact, the water from most sinks is already close enough to room temperature that we don’t need to leave it out overnight. If a few drops of water are spilled on the desk, they will slowly evaporate and turn to water vapor. The water drops will disappear. No heat was added, water just does that slowly, all by itself. The water in the container will take a lot longer to evaporate. In fact, it might take weeks, or even months for room temperature water to evaporate and turn to a gas. Evaporation is when water turns to a gas without any added heat.
Identify: What is evaporation?
We can add heat to the container of water by pouring it into a pot and putting it on the stove. When we turn the stove on high, heat moves from the stove, through the pan, and into the water. As the temperature increase, the water at the bottom of the pan, closest to the heat source, turns to a gas and forms bubbles. These bubble rise to the surface of the water. This process is called boiling. The bubbles are bubbles of water vapor, a gas, and when they pop at the top, the water vapor escapes into the air of the room. Boiling is when heat is added to water to cause it to change into a gas.
Identify: What is boiling?
Remember: there are two ways that water can change into a gas. Evaporating is when water, without heat being added, changes into a gas on its own. When water’s temperature increases enough, it will boil, and turn to a gas much quicker.