Question

Which of the following describes a physical change that results from the addition of

Answer 1

Answer:

A melting ice cube.

Explanation:

Since we are adding thermal energy (we are adding heat), we raise the temperature of an object.

Condensation on a mirror is incorrect because we are cooling the temp.

Inflating a balloon is incorrect because we aren't transferring thermal energy.

Tearing paper is incorrect because we aren't applying thermal energy.

Answer 2

Answer:

The answer is a melting ice cube.

Explanation:

Thermal energy is also known as heat. Therefore, we are applying heat to something in order to change its physical state.

A physical state is changeable and does not chemically alter the substance. It only alters the appearance of the object/substance. Because we are applying thermal energy to change it, melting something is the best fit. When we melt something, thermal energy does it - even if it's room temperature. Here's why:

• Condensation on a mirror can occur when you take a very hot shower and the steam fogs the mirror up. This would seem correct because we are transferring thermal energy from the steam to the mirror. However, this does not physically change the mirror. It just adds to the current state - the condensation can easily be removed by wiping it off and the mirror is back to normal.
• Melting an ice cube by applying heat would alter the physical state. Originally, we had a solid. But, once we melt the ice cube, it becomes water - a liquid. This is not a chemical change because we froze water originally to place it in a solid state. We only reversed this change by melting it, so it is just a physical change.
• Inflating a balloon is changing the balloon, but it would not apply to this situation because we are not applying any heat to change it. We are only inflating it with air and expanding it - no thermal energy is applied as we can easily blow a balloon up with cold air as well.
• Tearing a piece of paper would not apply even though it is a physical change. We are not applying any heat in tearing the paper - we are only applying force. Force is not thermal energy, so tearing paper is not an example of a physical change using thermal energy.

Therefore, thermal energy is used to physically change the ice cube by melting it.