Changes in materials: reversible and irreversible (5-9 years)：練習題

What happens to the temperature of pure ice when it begins to melt at normal atmospheric pressure?

A sealed beaker containing \(50\text{ g}\) of ice is placed on a balance. When the ice completely melts into liquid water, what is the reading on the balance?

Which of these changes is irreversible, meaning the material cannot be easily changed back to its original state?

Which of the following processes involves a change of state directly caused by the removal (loss) of heat?

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

When ice is heated above \(0^{\circ}C\), it changes from a solid to a liquid. Is this process a physical change or a chemical change? Give one reason for your answer.

Rusting is a chemical change that occurs when iron reacts with specific substances in the environment. Name the two essential substances required for rusting to occur and explain how a coating of oil prevents an iron tool from rusting.

When a puddle of rainwater on the pavement gradually disappears on a sunny day without boiling, what scientific process has taken place?

A student carries out two simple investigations in a science classroom:

Activity 1: She tears a sheet of newspaper into small shreds.
Activity 2: With the teacher's supervision, she uses a match to set fire to a piece of dry wood until only grey ash remains.

(a) Identify whether Activity 1 is a physical change or a chemical change.
(b) Identify whether Activity 2 is a physical change or a chemical change.
(c) State which of the two activities produces a new substance with completely different chemical properties.

A student investigates how temperature changes affect the three states of matter.

(a) What happens to the speed of movement of particles when a substance absorbs heat energy?
(b) Complete the table by identifying the names of the two phase changes described below:

• Process X: A liquid turns into a gas smoothly from its surface at any temperature below boiling point.
• Process Y: A gas cools down and changes into a liquid.

(c) The student heats liquid paraffin wax until it melts, and then cools it back down to room temperature. Explain why melting and solidifying paraffin wax is classified as a reversible physical change.