Chemical Reactions and Changes

What is the main characteristic of a chemical reaction?

• The substance changes its form, like melting or freezing.

• The substance breaks into smaller pieces.

• The substance changes into a new and different material.

• The substance changes its location.

Which observation suggests a new gas is being produced during a chemical reaction?

• Water turning into steam when heated.

• Bubbles forming when a metal is placed in acid.

• Ice cubes shrinking in the sun.

• A liquid becoming cloudy when cooled.

Which of these is an example of a physical change, not a chemical change?

• A biscuit burning and turning black.

• Magnesium metal producing smoke when heated.

• Dry ice changing directly into a gas.

• Vinegar and baking soda fizzing.

What is a common sign that a chemical reaction is happening, often involving a change in energy?

• The material changes its shape.

• The material becomes colder or hotter.

• The material is cut into smaller parts.

• The material changes its position.

When you use an instant ice pack, it feels cold. What kind of chemical change causes this?

• A chemical change that releases heat.

• A chemical change that absorbs heat.

• A physical change that releases heat.

• A physical change that absorbs heat.

How do glow sticks produce light?

• They absorb light from the surroundings and then glow.

• They generate electricity which powers a small light.

• Two chemicals inside mix and react to release light.

• They contain a special type of paint that glows in the dark.

In chemistry, what is a precipitate?

• A liquid that changes color when mixed with another liquid.

• A gas that forms when two liquids are combined.

• A solid that forms and does not dissolve when two liquids are mixed.

• A type of rain that falls during a chemical reaction.

When green copper carbonate is heated, it changes into a black substance. What does this color change indicate?

• The copper carbonate is melting.

• A new substance has been formed.

• The copper carbonate is dissolving.

• The heat is making the copper carbonate glow.