Chemical Equations and Reactions Quiz

What does a subscript in a chemical formula tell you? How is that different from a coefficient?

Answer explanation

A subscript in a chemical formula indicates the number of atoms of an element in a molecule, while a coefficient shows the number of molecules. For example, in 2H2O, '2' is a coefficient (2 molecules) and '2' in H2 indicates 2 hydrogen atoms.

Tags

NGSS.MS-PS1-1

In the formula H₂O, how many total atoms are in one molecule? How would that change if the formula was 3H₂O?

Answer explanation

In H₂O, there are 2 hydrogen atoms and 1 oxygen atom, totaling 3 atoms per molecule. For 3H₂O, you multiply by 3, resulting in 9 atoms (3 x 3 = 9). Thus, 3H₂O has 9 total atoms.

Tags

NGSS.MS-PS1-1

Why do we never change the subscripts when balancing equations? What would happen if we did?

Answer explanation

We never change the subscripts when balancing equations because they represent the number of atoms in a molecule. Changing them alters the substance itself, leading to incorrect representations of the chemical reaction.

How do balanced chemical equations show the Law of Conservation of Matter?

Answer explanation

Balanced chemical equations demonstrate the Law of Conservation of Matter by ensuring that the number of atoms of each element is the same on both sides of the equation, indicating that matter is neither created nor destroyed in a chemical reaction.

Tags

NGSS.MS-PS1-5

How can you tell when a chemical equation is truly balanced? What should you check?

Answer explanation

A chemical equation is balanced when the number of atoms for each element is the same on both sides. Check that the coefficients in front of compounds ensure equal atom counts for all elements involved.

Tags

NGSS.MS-PS1-5

Think back to the steel wool lab. If iron and oxygen combine to make iron oxide, what must be true about the number of iron and oxygen atoms on each side of the equation?

Answer explanation

In a chemical reaction, the law of conservation of mass states that the number of atoms must be the same on both sides. Therefore, the number of iron and oxygen atoms in the reactants must equal the number in the products.

Tags

NGSS.MS-PS1-5

Why might the iron atoms be written as Fe and the oxygen as O₂ in a chemical equation? How does this affect balancing?

Answer explanation

Iron is written as Fe because it is a single atom, while oxygen is O₂ to indicate it exists as diatomic molecules. This affects balancing by ensuring the number of each type of atom is equal on both sides of the equation.

Tags

NGSS.HS-PS1-7

If we were to write a balanced equation for the steel wool reaction, what do you think it would look like? What would the reactants and products be?

Answer explanation

The balanced equation for the steel wool reaction is 4Fe + 3O2 -> 2Fe2O3. The reactants are iron (Fe) and oxygen (O2), and the product is iron(III) oxide (Fe2O3). This shows the oxidation of iron.

Which type of reaction is:

C₇H₁₆ + 10 O₂ → 7 CO₂ + 8 H₂O

• Synthesis
• Decomposition
• Single Displacement
• Combustion

Tags

NGSS.MS-PS1-2

Balance this equation
_Zn+_HCl-->_ZnCl₂ +_H₂

• 1,1,2,1
• 1,1,1,2
• 1,2,1,1
• 2,1,1,1

Tags

NGSS.MS-PS1-5