Chemical Reactions

Which of the following would be a chemical change?

• Burning paper

• Ripping paper

• Melting an ice cube

• Evaporating water

Answer explanation

Only burning paper produces new substances like smoke, soot, CO2, and H2O. It is also a permanent change. The rest do not change one substance into another.

Which of the following would also be a chemical change?

• You break a window with a baseball.

• You mow the lawn.

• A bike chain rusts after being left out in the rain.

• You cut your food into smaller pieces.

Which of the following would be physical change.

• You snap a twig in two.

• You burn leaves after raking.

• You mix baking soda and vinegar.

• Elephant toothpaste reaction.

Answer explanation

All changes here except (snapping a twig) permanently transform substances.

Which of the following would also be a physical change ?

• Firework explosion.

• Rotting apple decomposing

• Rusting abandoned car

• Freezing water

Answer explanation

Even though freezing water is a drastic change. It is a physical change because the substance is still water just in a different phase. It is also easily reversible.

The law of matter of conservation of mass states .....

• matter can be created but not destroyed.

• matter can neither be created nor destroyed.

• matter can be both created and destroyed.

• matter cannot be created but can be destroyed.

Answer explanation

Antoine LeVosier found that as many times as he reacted different chemicals together, he could also account for all the matter he started with and ended with. This showed that matter cannot be created or destroyed.

The atoms and molecules to the left side of the arrow are known as:

• Reactants

• Products

• Yields

• Subscript

The atoms and molecules to the right side of the arrow are known as the

• Reactants

• Yields

• Products

• Coefficient

Is this a properly balanced chemical equation?

• Yes

• No.

Answer explanation

Yes. It is balanced. There are equal amounts of each element on both sides of the equation.

Is this a properly balanced chemical equation?

• Yes

• No

Is this a properly balanced chemical equation?

• Yes

• No

Answer explanation

There are 4 oxygens on the reactant side but only 2 on the product side.