Counting Atoms and Balancing Chemical Equations

What is the formula for calculating the total number of atoms in a compound?

• Multiply the number of atoms by the atomic mass of each element.

• Add the number of atoms represented by the subscripts for each element.

• Count the number of elements in the compound.

• Subtract the number of atoms from the total mass of the compound.

Tags

NGSS.MS-PS1-1

What is the purpose of balancing chemical equations?

• To increase the speed of a chemical reaction.

• To obey the law of conservation of mass, which states that matter cannot be created or destroyed.

• To ensure that all reactants are used up completely.

• To make the equations look more complex.

Tags

NGSS.MS-PS1-5

What does it mean for a chemical equation to be balanced?

• It means that the number of atoms of each element is the same on both sides of the equation.

• It means that the total mass of reactants is greater than the total mass of products.

• It means that the reaction occurs at a faster rate than unbalanced equations.

• It means that the products are in a different state than the reactants.

Tags

NGSS.MS-PS1-5

What is the difference between a coefficient and a subscript?

• A coefficient indicates the number of atoms, while a subscript indicates the number of molecules.

• A coefficient indicates the number of molecules, while a subscript indicates the number of atoms in a molecule.

• A coefficient is used in chemical equations, while a subscript is used in mathematical equations.

• A coefficient is a constant value, while a subscript is a variable value.

When balancing equations, what can be placed to the left of a formula of a substance to make the equations balanced?

• A coefficient.

• A subscript.

• An exponent.

• A variable.

Tags

NGSS.MS-PS1-5

What does the term 'reactants' refer to in a chemical equation?

• The substances that undergo a chemical change, found on the left side of the equation.

• The products formed after a chemical reaction, found on the right side of the equation.

• The catalysts that speed up the chemical reaction without being consumed.

• The energy required to initiate a chemical reaction.

Tags

NGSS.MS-PS1-5

What does the term 'products' refer to in a chemical equation?

• The substances that are produced as a result of a chemical reaction, found on the right side of the equation.

• The starting materials that undergo a chemical reaction, found on the left side of the equation.

• The energy released during a chemical reaction.

• The catalysts that speed up a chemical reaction.

Tags

NGSS.MS-PS1-1

NGSS.MS-PS1-5

How many Oxygens are in the molecule (OH)₂?

• 1

• 2

• 3

• 4

Tags

NGSS.MS-PS1-1

What is a subscript in a chemical formula?

• A small number written to the right of a chemical symbol that indicates the number of atoms of that element in a molecule.

• A large number written to the left of a chemical symbol that indicates the total number of molecules present.

• A symbol that represents the charge of an atom in a chemical reaction.

• A notation used to indicate the state of matter of a substance in a chemical equation.

How many O's are in Al₂(SO₄)₃?

• 10

• 12

• 8

• 14