Student Exploration: Chemical Changes
Vocabulary: acid, base, catalyst, chemical change, coefficient, conservation of matter, decomposition, dissolve, double replacement, endothermic, exothermic, indicator, ion, physical change, product, reactant, single replacement, subscript, synthesis
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
A student mixes baking soda and vinegar in a glass. The results are shown above. Do you think any new substances are being created in this mixture? If so, how do you know.
Suppose this was done on top of a balance. Do you think the mass would change as the reaction proceeded?.
What do you think would happen to the mass if the reaction took place inside a sealed plastic bag
A chemical change, (or chemical reaction) occurs when one or more substances, called reactants, are transformed into different substances, or products. In the Chemical Changes Gizmo, you will look for evidence of chemical changes by looking at changes you can see, touch, or smell.
To begin, check that Reactant 1 is Sodium and Reactant 2 is Water. Sodium is a metal so soft you can cut it with a knife.
Click Play (). What do you observe?
Do you think a chemical reaction has taken place? Explain.
Observing chemical changes
Get the Gizmo ready:
· Click Reset (). Check that the reactants are still Sodium and Water.
· Turn on the Label reactants checkbox.
Introduction: It is important to distinguish chemical changes, in which new substances are formed, from physical changes, which do not create new substances. In this activity, you will look at many kinds of evidence that chemists use to see if a chemical change has taken place.
Question: What kinds of evidence indicate a chemical change has taken place?
Observe: Some chemical reactions release heat, and others absorb heat. In an exothermic reaction, heat is released and the temperature of the system rises. In an endothermic reaction, heat is absorbed and the temperature of the system decreases.
In the Gizmo, drag the Thermometer into the flask of water.
What is the starting temperature
Click Play, and wait for the reaction to end. What is the final temperature?
Was this reaction exothermic or endothermic?