Question

Why is the burning of candles a chemical change?
A. Change in mass
B. Formation of new products
C. Original properties are changes
D. All of above

Answer 1

Hint: Burning of candle is both physical and chemical change. When we light the candle wax acts as fuel which is a chemical substance called carbon.

Step by step solution:
When we light the candle, the wax present near the wick will melt. Wick absorbs the liquid wax. The liquid wax evaporates due to the heat produced by the flame. Burning is a chemical change that involves oxidation thus producing heat and light. When a candle is burnt in air, the mass of the product is increased due to atmospheric oxygen which combines with the carbon and hydrogen of the candle wax during burning to produce water vapor and carbon dioxide. Also the properties of the reactants are altered. And this is an irreversible change. Here, the chemical reaction of burning candle is:
$$C_x{H}_y+(x+\frac{y}{4})O_2\stackrel{}{\to }(y/2)H_{2}O+(x)C{O}_2$$
Here, $$x=n,y=2n+2$$.
From the above explanation we can say that formation of new products (carbon dioxide and water) takes place, by the addition of oxygen mass of product will increase and original properties of wax will change . So, we can say option D is correct.

Additional information: On heating, candle wax melts and forms liquid wax. So, it is a physical change in the burning of candles. Since, it again turns into solid wax on cooling. This is a reversible change.

Note: Here the chemical formula wax can be different i.e. different type waxes have different chemical formulas. And the chemical equation says nothing about the existence of a flame.