Molecules, Atoms, and Balancing Equations Review

Henry is looking at a glass of water and wonders about the tiny particles inside. Which statement best describes the difference between an atom and a molecule in the water?

• An atom is made of many molecules, while a molecule is a single particle.

• An atom is a single type of particle, while a molecule is two or more atoms bonded together.

• Atoms and molecules are the same thing with different names.

• Molecules are always larger than atoms and contain metals only.

Nora is studying the chemical formula CH2CO in her chemistry class. She wants to know how many carbon (C) atoms are present in one molecule of CH2CO. Can you help her?

• 1

• 2

• 3

• 4

Emma is conducting an experiment and uses a chemical with the formula C2H3NaO2. What is the total number of hydrogen atoms in one molecule of this chemical?

• 1

• 2

• 3

• 4

Elijah is preparing a science experiment and needs to use 3 SO2 molecules. What does the coefficient 3 indicate?

• There are three types of atoms in SO2.

• There are three sulfur atoms in each SO2 molecule.

• There are three separate SO2 molecules.

• The subscript 2 should be multiplied by 3 to give SO6.

Hannah burns a piece of wood in a closed container. After the reaction, she weighs the container and finds that the total mass is the same as before. Which statement best describes what happened according to the Law of Conservation of Mass?

• Mass can be created during chemical reactions but not destroyed.

• Mass is destroyed when products are formed.

• Matter cannot be created or destroyed in a chemical reaction; atoms are rearranged.

• Only the number of molecules stays the same during reactions, not atoms.

Grace is performing an experiment where she splits water into hydrogen and oxygen gases: 2 H2O → 2 H2 + O2. Which option explains why this follows the Law of Conservation of Mass?

• There are more molecules on the product side.

• The total number of H and O atoms is the same on both sides of the equation.

• Mass is lost because a gas is produced.

• Water molecules are destroyed and not replaced.

Luna is mixing iron (Fe) and sulfur (S) in a lab to create iron sulfide (FeS). She writes the equation Fe2 + S2 → 2 FeS on the board. Is this equation balanced?

• Yes, because there are equal numbers of Fe and S atoms on both sides.

• No, because there are more Fe atoms in the products than in the reactants.

• No, because there are more S atoms in the products than in the reactants.

• Yes, because the total number of molecules is the same on both sides.

Elijah is conducting a chemistry experiment and writes the equation 2 Ag + 6 HCo → 2 AgCo3 + 3 H3 on the board. Which statement correctly identifies the issue with his equation?

• It is balanced as written.

• Silver (Ag) atoms are not conserved.

• Hydrogen atoms are not conserved.

• Cobalt atoms are not conserved.

Priya puts an ice cube in a glass and watches it melt into water. Which statement best describes what happens to the ice cube?

• A new substance forms with different properties.

• Matter changes state, shape, or size but stays the same substance.

• Gas is produced with a new smell.

• Energy is released as light from a reaction.

Charlotte is baking a cake and notices bubbles forming and a new smell coming from the batter. Which is a common sign of a chemical change?

• Change in shape only

• Dissolving without new substances

• Formation of a new solid, liquid, or gas

• Melting of a solid