Chapter 2 - Chemistry

Ava is observing different processes in her science class. Which of the following processes is a physical change?

• ice melting into water

• iron rusting over time

• wood burning in a fire

• milk turning sour

Answer explanation

Ice melting into water is a physical change because it involves a change in state from solid to liquid without altering the chemical composition. The other options involve chemical changes.

Why does a metal block weigh more than a wooden block of the same size?

• elasticity

• hardness

• density

• flexibility

Answer explanation

A metal block weighs more than a wooden block of the same size because metal has a higher density. Density is the mass per unit volume, and since metals are generally denser than wood, they weigh more for the same volume.

What type of mixture is unsweetened tea?

• a homogeneous mixture

• a heterogeneous mixture

• a compound

• a pure substance

• an element

Answer explanation

Unsweetened tea is a homogeneous mixture because the tea leaves are fully dissolved in water, creating a uniform composition throughout. Unlike heterogeneous mixtures, the components are not visibly distinct.

This picture is an example of

• diatomic elements

• endothermic reactions

• isothermic reactions

• exothermic reactions

How many sulfur atoms are there in one formula unit of Al₂(SO₄)₃?

• 1

• 2

• 3

• 4

Answer explanation

In Al₂(SO₄)₃, there are 3 sulfate ions (SO₄) per formula unit. Each sulfate ion contains 1 sulfur atom, so 3 sulfate ions contribute 3 sulfur atoms in total. Therefore, the correct answer is 3.

A mixture that consists of two or more materials in distinct phases is called __________.

• homogeneous

• heterogeneous

• uniform

• consistent

Answer explanation

A mixture with distinct phases, where components are not uniformly distributed, is termed heterogeneous. In contrast, homogeneous mixtures have a uniform composition throughout.

The pictures are examples of

• endothermic reactions

• physical changes

• ectothermal reactions

• exothermal reactions

The measure of the dispersal of energy in a system is known as __________.

• energy

• entropy

• enthalpy

• none of these

Answer explanation

The measure of the dispersal of energy in a system is known as entropy. It quantifies the amount of disorder or randomness, making it the correct choice over energy and enthalpy, which refer to different concepts.

Label the number with the correct term.

a

b

superscript

multiplier

coefficient

subscript

Heat is the term used for the movement of __________ energy.

• thermal

• kinetic

• potential

• increased

Answer explanation

Heat refers to the transfer of thermal energy, which is the energy associated with the temperature of an object. Therefore, the correct answer is 'thermal'.