Item SB058001: If the characteristic properties of the ending substances are different than the characteristic properties of the starting substances, a chemical reaction occurred. (This item used a table to show the properties of the substances.)

A scientist performs two experiments. Before conducting the experiments, she determines the characteristic properties of each of the starting substances. In the first experiment, she heats a liquid (Liquid 1), and a gas (Gas 1) forms. In the second experiment, she passes an electric current through a different liquid (Liquid 2), and two gases (Gas 1 and Gas 2) form. After the experiments, the scientist determines the properties of each of the ending substances. The table below summarizes her findings for each experiment.

Experiment 1 Color Melting Point (ºC) Boiling Point (ºC)
Before heating Liquid 1 Colorless -114 78
 
After heating Gas 1 Colorless -114 78
 
Experiment 2 Color Melting Point (ºC) Boiling Point (ºC)
Before electric current Liquid 2 Colorless 0 100
 
After electric current Gas 2 Colorless -219 -183
Gas 3 Colorless -259 -253

Did a chemical reaction occur during either of these experiments? Explain.

  1. A chemical reaction occurred during both of these experiments because matter changed during each experiment and all changes to matter involve chemical reactions.
  2. A chemical reaction occurred during both of these experiments because the scientist will not be able to turn the gases back into the liquids in either experiment and chemical reactions are irreversible changes.
  3. A chemical reaction occurred only during Experiment 1 because heat was used during Experiment 1 and chemical reactions require heat in order to occur.  Experiment 2 did not involve heating, so a chemical reaction did not occur.
  4. A chemical reaction occurred only during Experiment 2 because Gases 2 and 3 have different properties than Liquid 2 and new substances with different properties always form during chemical reactions.  In Experiment 1, Gas 1 has the same properties as Liquid 1, so a chemical reaction did not occur.
  5. A chemical reaction did not occur during either experiment because a chemical reaction requires at least two starting substances and there is only one starting substance in each experiment.
  6. A chemical reaction did not occur during either experiment because the starting substances and ending substances of each experiment are all colorless substances and a color change must occur in order for it to be a chemical reaction.