What are some common mistakes students make with changes of state?

1 Answer

One common error is that students commonly identify dissolving as a chemical change rather than a physical change.

The confusion probably is most linked with a process like the dissolving of salt.

NaCl(s) -> Na+(aq) + Cl-(aq)

There are chemical bonds (ionic) between the sodium ions and chloride ions that are being broken in this process, but NO NEW bonds are formed. That makes this process a physical change.

Another reason this is a physical change is that a physical process (boiling or evaporation) could separate the salt and the water.