Chemical Reactions: Signs and Types Worksheet

Question 1

A student mixes vinegar and baking soda in a cup. The mixture bubbles and foams. What sign of a chemical reaction is shown, and what does it tell you?

Accepted Answer

The bubbling and foaming show that a gas is being produced. Gas production is evidence that a chemical reaction has occurred.

Question 2

When a piece of iron is left outside for many weeks, reddish-brown rust forms on its surface. Is this a physical change or a chemical reaction? Explain your answer.

Accepted Answer

Rusting is a chemical reaction because a new substance, rust, forms on the iron. The color change and new material are evidence of a chemical reaction.

Question 3

Classify this reaction as synthesis, decomposition, single replacement, double replacement, or combustion: magnesium plus oxygen forms magnesium oxide.

Accepted Answer

This is a synthesis reaction because two substances, magnesium and oxygen, combine to form one new compound, magnesium oxide.

Question 4

Classify this reaction as synthesis, decomposition, single replacement, double replacement, or combustion: hydrogen peroxide breaks down into water and oxygen gas.

Accepted Answer

This is a decomposition reaction because one compound, hydrogen peroxide, breaks apart into simpler substances, water and oxygen gas.

Question 5

A candle burns in oxygen and produces carbon dioxide, water vapor, heat, and light. What type of reaction is this? Give one piece of evidence that a chemical reaction occurred.

Accepted Answer

This is a combustion reaction because a substance burns in oxygen and releases energy. Heat and light are evidence that a chemical reaction occurred.

Question 6

Two clear liquids are mixed in a test tube. A cloudy white solid appears and settles at the bottom. What sign of a chemical reaction is shown?

Accepted Answer

The formation of a cloudy white solid shows that a precipitate formed. A precipitate is a new solid substance made during some chemical reactions.

Question 7

Classify this reaction as synthesis, decomposition, single replacement, double replacement, or combustion: zinc metal reacts with hydrochloric acid to form zinc chloride and hydrogen gas.

Accepted Answer

This is a single replacement reaction because zinc replaces hydrogen in the acid, forming zinc chloride and hydrogen gas.

Question 8

Classify this reaction as synthesis, decomposition, single replacement, double replacement, or combustion: silver nitrate reacts with sodium chloride to form silver chloride and sodium nitrate.

Accepted Answer

This is a double replacement reaction because the positive and negative parts of two compounds switch partners to form two new compounds.

Question 9

A student mixes two room-temperature solutions. The cup becomes noticeably warmer, but no flame appears. What sign of a chemical reaction is shown?

Accepted Answer

The temperature increase shows that energy was released during the reaction. A temperature change can be evidence that a chemical reaction occurred.

Question 10

A glow stick is bent and shaken. It begins to glow without being plugged in or heated. What sign of a chemical reaction is shown?

Accepted Answer

The glow stick gives off light, which is a sign that a chemical reaction is occurring. The chemicals inside react and release energy as light.

Question 11

Decide whether this change is most likely physical or chemical: An ice cube melts into liquid water. Explain your answer.

Accepted Answer

Melting ice is a physical change because the substance is still water. No new substance is formed.

Question 12

Decide whether this change is most likely physical or chemical: A piece of paper turns black and gives off smoke when it burns. Explain your answer.

Accepted Answer

Burning paper is a chemical reaction because new substances, such as ash, smoke, and gases, are formed. The color change, gas production, and release of heat are evidence.

Question 13

Look at this word equation: calcium carbonate produces calcium oxide plus carbon dioxide. What type of reaction is it, and what sign might you observe?

Accepted Answer

This is a decomposition reaction because one compound breaks down into two products. A possible sign is gas production because carbon dioxide gas is formed.

Question 14

A blue copper chloride solution is added to a piece of aluminum foil. After a few minutes, the foil looks darker and a reddish solid appears. What evidence suggests a chemical reaction occurred?

Accepted Answer

The color change and formation of a reddish solid suggest that a chemical reaction occurred. These signs show that new substances formed.

Question 15

Write one original example of a chemical reaction and identify at least two signs that would show the reaction happened.

Accepted Answer

One example is burning wood. Signs include heat and light being released, smoke or gas forming, and ash being produced as a new substance.

Chemical Reactions: Signs and Types

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