Question

apply it
talk about it
think about other examples that involve both physical and chemical changes, and share them with your group.

1. theme distinguish what physical and chemical changes are involved in burning a candle? use the table below to give examples and distinguish between physical change and chemical change.

table with columns: change, chemical or physical, reason

1. sep engage in argument you and a friend are using colored markers and white posterboard to make posters for a science fair at school. your friend says that a chemical change occurred because the markers changed the color of the posterboard. do you agree? explain why or why not.

Explanation:

Question 1

To answer this, we analyze the changes in a burning candle:

• Melting of Wax: This is a physical change. The reason is that the wax changes from solid to liquid (state change) but its chemical composition (it's still wax, \( C_{n}H_{2n + 2}\) - type hydrocarbons) remains the same. No new substance is formed.
• Burning of Wax (Combustion): This is a chemical change. The wax reacts with oxygen (\( \text{Wax} + O_{2}\xrightarrow{\text{Heat}} CO_{2}+H_{2}O+\text{Energy}\)) to form new substances (carbon dioxide, water vapor) and releases energy. A chemical reaction (combustion) occurs, changing the chemical identity of the wax.

We can fill the table as follows:

Change	Chemical or Physical	Reason
Burning of wax (combustion)	Chemical	Wax reacts with oxygen to form new substances (e.g., \( CO_{2}\), \( H_{2}O\)) and releases energy; a chemical reaction occurs.

To determine if a chemical change occurred when using markers on posterboard, we recall the definition of chemical and physical changes:

• A chemical change involves the formation of new substances with different chemical properties (e.g., rusting, combustion).
• A physical change involves a change in appearance (color, state, shape) without forming new substances (e.g., melting, mixing, color change from pigment deposition).

When markers are used on posterboard, the ink from the markers adheres to the surface of the posterboard. The color change is due to the ink (pigments) being deposited on the posterboard. The chemical composition of the posterboard (paper, typically cellulose) and the ink (dyes/pigments + solvents) do not undergo a chemical reaction to form new substances. The ink can potentially be removed (e.g., with solvents), and the posterboard remains chemically the same. Thus, this is a physical change, not a chemical change.

Answer:

Change	Chemical or Physical	Reason
Burning of wax	Chemical	Wax reacts with \( O_2\) to form \( CO_2\), \( H_2O\), new substances.

Question 2