U1L1-L5 Intro, Matter, Mass, Volume, Density

This image shows a

• chemical reaction

• physical change

• musical change

• all of these answers are correct

Answer explanation

A chemical reaction involves a change to a substances chemical identity (the specific molecules that make the chemical)

This change is

• a chemical reaction

• a physical change

• a snowman's nightmare

• irreversible

Answer explanation

Ice melting is physical change because the molecules (H₂O) are the same, only the phase of the water is changing, from solid (s) to liquid (l).

A copper penny turning greenish after a few years outside is an example of a

• Chemical Change

• Physical Change

• Small Change

• Centsless Change

Answer explanation

It is a chemical change. Copper reacts with oxygen and carbon dioxide from the air in the presence of water, and can form a variety of compounds, some of which have blue or green colors. This means that the chemical identity (the specific molecules that make the chemical) has changed.

A candle wick burning is an example of a _________________________

• physical reaction

• condensation

• emotional reaction

• chemical reaction

Answer explanation

Anything about combustion or flammability is a chemical change, as the chemical identity of what makes up the materials are changed.

When candle wax melts, it is a ___________________ change.

• chemical

• physical

• transparent

• undefined

Answer explanation

The chemical composition of the wax has not changed when melting, it just changed from a solid to a liquid.

A teacher is demonstrating physical and chemical changes to her class. Which action should she use to demonstrate a chemical change?

• cutting a piece of paper

• folding a piece of paper

• tearing a piece of paper

• burning a piece of paper

Answer explanation

Anything about combustion or flammability is a chemical change, as the chemical identity of what makes up the materials are changed.

When food and the air react there is a

• physical change

• chemical change

• gross change

Answer explanation

Anything involving a reaction is a chemical change, as the chemical identity of what makes up the materials are changed.

One component of an alka-seltzer table is sodium bicarbonate, NaHCO₃. When placed in water this happens. What type of change is this?

• Chemical change

• Physical change

• Plop change

• Fizz change

Answer explanation

Another component of alka seltzer is citric acid, which reacts with the sodium bicarbonate to produce carbon dioxide gas, and some other things. Anything with a chemical reaction is a chemical change.

Is this a chemical or a physical change?

• Chemical change

• Physical change

Answer explanation

There is no chemical reaction, both pieces are still paper.

Is liquid water freezing a physical or chemical change?

• physical

• chemical

• it is fake news

Answer explanation

Water melting and boiling is a physical change, not a chemical change. The molecules (H2O) are not changed, they just exist as a solid, liquid or gas.