Chemical Changes & Reactions

Which of the following models best demonstrates a balanced chemical equation?

• F
• G
• H
• J

Coal contains carbon and other elements. Carbon dioxide forms when coal burns in the presence of oxygen. Which of these is the best evidence that a chemical reaction occurs when coal burns?

• The shape of the coal changes
• Oxygen is present
• A new substance is produced
• Coal is made up of more than one element

_________ is (are) made of more than one atom.

• A molecule
• Protons
• Neutrons
• An element

Which is an example of a physical change?

• Burning wood
• Freezing water
• Rust on a car
• Cooking food

the starting materials in a chemical reaction

• Products
• Reactants
• Starters
• Enders

Which of Mark’s observations would show that a burning candle is a chemical reaction?

• Black smoke is given off; hot gases are rising.

• The wax starts to melt.

• The candle is white and made of wax and a wick.

• Time passes one minute at a time.

When two or more different elements are chemically combined.

• Mixture

• Element

• Solution

• Compound

Select the substances that are the reactants in the following chemical formula:  $CH_{4\ }+2O_2\ \rightarrow\ CO_2+\ 2H_2O$  

• $2H_2O$

• $2O_2$

• $CH_4$

• $CO_2$

How many Hydrogen (H) molecules are in  $2H_2O$  ?

At the end of chemical reactions, what is the total mass of the reactants compared to the total mass of the products?

• the product is doubled
• the product is half the mass of the reactants
• the mass is the same
• the mass changes depending on the reaction