1.7 Physical & Chemical Changes Pages 28 – 30 of the text

The burning candle… When we observe a candle burning we can see physical and chemical properties and we can also witness physical and chemical changes. Physical changes are the ones that the substance changes some, but not completely.  When the wax melts from the top and drips down the side (solid → liquid → solid) it’s still wax

Chemical changes are those that have the substance becoming something completely different and it can’t be returned to the starting state.  When the candle is burning and some of the wax changes into carbon dioxide and gives off energy, that is a chemical change. The wax won’t return and the energy is used up (heat & light).

Physical Change Physical changes usually can be identified by seeing that the state or form have changed but the substance itself is still the same.  Examples would include: water melting, water freezing, water evaporating, water condensing, cutting something into pieces, dissolving sugar in water Can you think of any?

Chemical Change Chemical changes are the ones where the substance is changed into one or more different things and the reactions can’t be reversed.  Examples would include: brass tarnishing, metal rusting, cooking something or burning something.

Table 2 Page 30 When trying to decide if a change is physical or chemical you must examine lots of things. Let’s look at Table 2 and copy it into the notebook.  The book shows that change in colour, heat or light being produced, bubbles being formed, precipitate being formed and irreversible changes may all indicate chemical change. When might some of those things not be true?

Questions Do questions 2, 4 and 5 on page 30.  In question 5 you need to look back at scenario 3 on page 13, list all of the changes occurring and then tell which things happening at the campfire are physical changes and which are chemical.