Question

Two chemicals react in an endothermic reaction. What can be known about this reaction?

Heat is absorbed because the old substance needs more energy to break its bonds.
Heat is released because the old substance needs less energy to break its bonds.
A precipitate will form as a result of the reaction.
A gas will form as a result of the reaction.


For a science project, Janet performs four experiments that are supposed to show a chemical reaction. She displays her results in a table.

A 4-column table with 4 rows. The first column titled experiment has entries 1, 2, 3, 4. The second column titled substances has entries water + heat, vinegar + baking soda, cabbage juice + lemon juice, liquid A + liquid B. The third column titled evidence of reaction has entries gas formation, gas formation, color change, precipitate formation. The fourth column titled Chemical Reaction ? has entries yes, yes, yes, yes.

In the column titled "Chemical reaction?,” which experiment’s data should be changed to "No”?

Experiment 1
Experiment 2
Experiment 3
Experiment 4



When liquid silver nitrate and liquid sodium chloride are combined, solid silver chloride forms along with a new liquid, sodium nitrate. Which substance represents the precipitate?

silver nitrate
silver chloride
sodium chloride
sodium nitrate


Which is evidence that a chemical reaction has likely occurred?

a liquid slowly losing volume
the formation of a precipitate
boiling water releasing steam
a change in the shape of a solid



Which is an example of a chemical reaction?

paper folded into tiny pieces
paper burned and turned into smoke
paper soaked in water
paper shredded and turned into pulp

Answer 1

1) Two chemicals react in an endothermic reaction. What can be known?
- Heat is absorbed because the old substance needs more energy to break its bonds. (True)
- All other choices are false (endothermic means heat is absorbed; it does not guarantee a precipitate or gas).

2) In Janet’s table, which experiment’s "Chemical reaction?" should be changed to "No"?
- Experiment 1 (water + heat → gas is just boiling/evaporation, a physical change, not a chemical reaction)

3) When AgNO3 and NaCl are combined, which is the precipitate?
- Silver chloride (AgCl)

4) Which is evidence that a chemical reaction has likely occurred?
- The formation of a precipitate

5) Which is an example of a chemical reaction?
- Paper burned and turned into smoke