Students who demonstrate understanding can: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Clarification statement: Examples of reactions could include burning sugar or steel wool, fat reacting with sodium hydroxide, and mixing zinc with hydrogen chloride.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
When two substances interact, something new may or may not form. The test is the properties. If the substances you end up with have different characteristic properties from the ones you started with, such as a new melting point, density, solubility, odor or color, then the atoms have rearranged into new substances and a chemical reaction has happened.
Students work with data tables rather than guesses. Burning sugar leaves a black solid that does not dissolve in water and does not taste sweet, so it is a new substance. Zinc dropped into hydrochloric acid gives off a gas that pops with a lit splint, which neither starting material does on its own. In contrast, melting butter or dissolving salt changes the appearance, but the melting point and other properties of the substance stay the same, so no new substance formed.
The skill is to compare before and after, property by property, and to argue from the data rather than from a single dramatic observation such as fizzing or a color change.
Boiling water bubbles and so does a shaken soda, yet no new substance forms. Ask students what the gas is and whether its properties differ from the starting materials.
Sugar seems to disappear in water, but evaporating the water returns sugar with the same properties. Dissolving is a physical change that forms a mixture.
Cutting steel wool or crushing a sugar cube changes size and shape, but those are not characteristic properties. Density and melting point stay the same.
Students may say the reactants vanish. The atoms are all still there; they have been rearranged into different substances.
Steel wool is gray, shiny, bends easily and is attracted to a magnet. After it is burned, the product is dark, brittle, crumbles when touched and is only weakly attracted to a magnet. Did a chemical reaction occur?
Answer: Yes. The product's properties (color, brittleness, magnetic behavior) differ from those of steel wool, so a new substance formed and a chemical reaction occurred.
Set up stations where students record properties before and after: baking soda and vinegar, ice melting, sugar dissolving, a candle burning. Make them fill in the same columns for each so the comparison is honest, then sort the stations into reactions and non-reactions with evidence.
Tests typically present a data table with density, melting point and solubility for substances before and after mixing and ask which change shows a reaction. Train students to look for a substance after mixing whose properties match none of the starting substances.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: A) A new substance formed, so a chemical reaction occurred
A solid with properties unlike either starting material is a new substance, which is the evidence for a chemical reaction.
Answer: D) Ice melting into water
Melted ice is still water with the same properties. The other three changes produce substances with new properties.
Answer: characteristic properties (also accepted: characteristic, characteristic property)
Characteristic properties stay the same for a pure substance no matter how much of it you have, so they can be used to identify it.
Answer: B) Whether the gas and any other products have properties different from the starting substances
Bubbles are a clue. The evidence is whether new substances with different properties have formed.
Answer: A) A physical change
The salt was recovered unchanged, so no new substance formed. Dissolving is a physical change.
Answer: rearranged (also accepted: rearranged into new substances)
The same atoms are present before and after. They are regrouped into different substances.
Make observations and measurements to identify materials based on their properties.
Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
A full lesson with slides, activities and an exit ticket on evidence of a chemical reaction, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-PS1-2 with an answer key, ready in about a minute.
Make a worksheet βTurn evidence of a chemical reaction into a quiz students answer online that marks itself, with a class summary for you.
Build a test βData on characteristic properties, such as density, melting point, solubility, flammability or odor, measured before and after the substances interact. A change in these properties shows a new substance.
No. Food coloring spreading through water changes the color without making a new substance. Color change is a clue to investigate, not proof on its own.