Question 1

Which of the following is an example of a physical change?

Accepted Answer

Water boiling and being converted into steam is a physical change because it involves a change in state (from liquid to gas) without a change in the chemical composition of water.

Question 2

Which of the following is an example of a chemical change?

Accepted Answer

Gasoline being used in the engine of a car producing exhaust is an example of a chemical change, as the hydrocarbons in the gasoline are reacting with the oxygen in the air to produce carbon dioxide, water vapor, and other products.

Question 3

The boiling point of methanol is 65°C and the boiling point of ethanol is 78°C.Which of the following statements is true?

Accepted Answer

At a temperature of 70°C, methanol would be in a gaseous state while ethanol would still remain in its liquid state. Since the boiling point of methanol is lower than that of ethanol, it would boil off before ethanol. Therefore, at 70°C, you would have methanol gas and liquid ethanol. Option A is the only option that states this fact. The other options are incorrect.

Question 4

Is the following transformation representative of a physical change or a chemical change?

Accepted Answer

The fact that the atoms are connected differently suggests that there has been a chemical change, as new compounds are formed through chemical reactions.

Question 5

What chemical change occurs when a wax candle burns?

Accepted Answer

When a wax candle burns, the heat of the flame melts the wax near the wick. This liquid wax is then drawn up the wick to the heat source, where it eventually vaporizes and reacts with oxygen in the air. This reaction produces heat, light, water vapor, and carbon dioxide, and represents a chemical change. The products of this reaction (water vapor and carbon dioxide) are different from the wax and oxygen used as reactants, so this represents a chemical change rather than a physical change.

Question 6

Each night you measure your height just before going to bed.When you arise each morning,you measure your height again and consistently find that you are 1 inch taller than you were the night before but only as tall as you were 24 hours ago! Is what happens to your body in this instance best described as a physical change or a chemical change?

Accepted Answer

This is a physical change because it involves a change in height due to the compression and decompression of the spine over the course of the day. It readily reverses when your body decompresses overnight, causing you to be slightly taller again in the morning. There is no chemical reaction occurring in this instance. Choice A and C are incorrect because they involve chemical changes, which are not occurring in this scenario, and choice D is irrelevant to the question being asked.

Question 7

Which of the following would be considered a chemical property?

Accepted Answer

Reactivity towards water is a chemical property because it involves how a substance reacts with another substance on a molecular level. Melting and boiling temperatures, conductivity, and flexibility are physical properties that do not involve chemical reactions.

Question 8

A chemical change involves the formation or breaking of

Accepted Answer

A chemical change involves the rearrangement of atoms and the forming or breaking of chemical bonds, which are not present in A or B. Therefore, the correct choice is C.

Question 9

Classify the following changes as physical or chemical.Wood burns to ashes; water begins to boil; grass grows; a rock is crushed to powder.

Accepted Answer

- Wood burning to ashes is a chemical change.
- Water boiling is a physical change.
- Grass growing is a chemical change.
- A rock being crushed to powder is a physical change.

Question 10

Is aging primarily an example of a physical or chemical change?

Accepted Answer

Aging involves the chemical reformation of biomolecules such as DNA, proteins, and lipids which contribute to the physical changes we observe in our bodies. Therefore, aging is primarily an example of a chemical change.

Question 11

A sample of iron weighs more after it rusts because

Accepted Answer

Rust is formed when iron reacts with oxygen in the presence of water, which results in the formation of hydrated iron(III) oxide, or rust. As rust is formed, oxygen is added to the iron, leading to an increase in mass. Therefore, the correct answer is C - the additional oxygen it contains. Option A is incorrect as rust forms within the iron lattice, which doesn't increase the volume of iron. Option B is incorrect as rust doesn't contain twice as many iron atoms, in fact, it contains fewer iron atoms than pure iron. Finally, option D is incorrect as iron weighs more after rusting, not less.

Question 12

Which of the following would be considered a physical property?

Accepted Answer

Density is a physical property because it is a characteristic of a substance that can be observed or measured without changing the substance's identity or composition. Flammability, corrosion resistance, reactivity towards acid, and oxygen sensitivity are all chemical properties because they describe how substances react and change chemically.

Question 13

A chemical change results in

Accepted Answer

A chemical change involves the rearrangement of atoms and the formation of new chemical compounds, resulting in the creation of new materials with different properties than the original substances.

Question 14

Water and ethanol can be separated by heating the ethanol until it boils away from the water.What type of change is this?

Accepted Answer

This is a physical change because it does not involve a change in the chemical composition of either substance. Heat is simply being applied to separate the two substances based on their different boiling points.

Question 15

In the winter Vermonters make a tasty treat called "sugar on snow" in which they pour boiled-down maple syrup onto a scoop of clean fresh snow.As the syrup hits the snow it forms a delicious taffy.Which of the following changes are involved in the making of sugar on snow?

Accepted Answer

All of the above changes are involved in the making of sugar on snow. Boiling down the maple syrup involves the evaporation of water, the syrup warms the snow causing it to melt while the syrup becomes more viscous, and as the maple syrup is boiled, the sugar within the syrup begins to caramelize, which is an example of a chemical change. Therefore, option D is the correct choice.

Question 16

Based on the information given in the following diagrams,which substance has the lower boiling point: one made from molecule A or one made from molecule B?

Accepted Answer

The answer of Based on the information given in the...

Question 17

Which of the following would not be considered a physical property?

Accepted Answer

The temperature at which a material catches on fire is a chemical property, not a physical property. Physical properties are characteristics that can be observed or measured without changing the identity of the substance, while chemical properties describe how a substance reacts with other substances to form new ones.

Question 18

Oxygen, O₂ ,is certainly good for you.Does it follow that if small amounts of oxygen are good for you then large amounts of oxygen would be especially good for you?

Accepted Answer

Breathing pure oxygen for extended periods of time can actually be harmful to the body. It can lead to an overproduction of oxygen free radicals which can damage cells and tissues, as well as causing problems with the body's nitrogen balance. This is why oxygen therapy is typically only given for short periods of time under medical supervision.

Question 19

A skillet is lined with a thin layer of cooking oil followed by a layer of unpopped popcorn kernels.Upon heating the kernels all pop thereby escaping the skillet.Which of the following physical and/or chemical changes occurred?

Accepted Answer

Heating the water in the kernel to the point of vaporization is a physical change, while the cooking of starches is a chemical change. Both of these changes occur during the popping of the kernels. Physical and chemical changes can occur without a chemical reaction.

Question 20

Which of the following would not be considered a chemical property?

Accepted Answer

The boiling point is a physical property, not a chemical property. Chemical properties relate to a substance's ability to undergo chemical reactions or changes, such as rusting or dissolving. Light sensitivity and explosiveness are also examples of chemical properties.

Quiz 14: Elements of Chemistry