Praxis Elementary Education Exam—States of Matter - dummies

# Praxis Elementary Education Exam—States of Matter

The Praxis Elementary Education exam will usually contain questions about the basic states of matter and how they can be affected by temperature and pressure.

Matter is in everything, from rocks to water to air, from mountains to microbes to mist; it comprises all objects and substance—anything that has mass and takes up space is matter.

As you can see in the table, there are three basic states of matter, with each state having specific properties regarding the shape it takes and the speed at which its molecules move.

Changes in temperature or pressure can cause a change in a state of matter. As temperature increases, molecules move faster. As pressure increases, molecules move slower.

• Melting: An increase in temperature making the molecules move faster; a solid may change to liquid, which may change to gas
• Freezing: A decrease in temperature making the molecules move slower; a gas may change to liquid, which may change to solid
• Boiling: When liquid, having reached its boiling point, changes to gas
• Sublimation: When a substance changes from a solid to gas, skipping the liquid state
• Deposition: When a substance changes from a gas to a solid, skipping the liquid state

A change in a state of matter, such as ice (solid) melting (becoming liquid), results in a physical change. The process can be reversed: The melted liquid can be frozen back into a solid. The substance is still water. When the substance of matter changes, it is a chemical change. A nail made of iron, when left outside long enough, will rust. The rust is made of iron and oxygen: The substance (iron) changed to iron and oxygen.

## Practice question

1. Which of the following is NOT true?
A. Burning wood is an example of a physical change.
B. On Earth, an empty glass is actually full.
C. Protons and neutrons are inside the nucleus of an atom.
D. Carbon dioxide is a compound.

## Answer and explanation

1. The correct answer is Choice (A).
It is a chemical change. When wood burns, new substances are formed (such as carbon dioxide and water vapor) that cannot be changed back. The ash in a fireplace where wood is burning cannot be changed back to wood. Choice (B) IS true because, on Earth, the glass has air in it, and air, as matter, takes up space (has volume). Choice (C) IS true. Choice (D) IS true because carbon dioxide, CO2, is one atom of the element carbon bonded to two atoms of the element oxygen.