Chemistry Final Exam Review

Match the following descriptions with the correct number of protons, neutrons, and electrons in a sodium ion (Na⁺).

• Sodium ion with more neutrons than protons, and fewer electrons

• 12, 11, 12

• Sodium ion with more neutrons than protons, and equal electrons

• 11, 12, 10

• Sodium ion with more protons than neutrons, and equal electrons

• 11, 12, 11

• Sodium ion with equal protons and neutrons, and more electrons

• 11, 11, 12

Answer explanation

A sodium ion (Na⁺) has 11 protons (atomic number), 12 neutrons (23 - 11), and 10 electrons (11 - 1 due to the positive charge). Thus, the correct choice is 11 protons, 12 neutrons, and 10 electrons.

Elements in the same group of the periodic table share similar properties because they have (a)  

• The same number of protons

• The same atomic mass

• The same number of valence electron

• The same number of electron shells

Answer explanation

Elements in the same group of the periodic table have the same number of valence electrons, which determines their chemical properties and reactivity. This is why they share similar characteristics.

In an exothermic reaction, energy is:

• Released to the surroundings

• Absorbed from the surroundings

• Created

• Destroyed

Answer explanation

In an exothermic reaction, energy is released to the surroundings as heat. This is why the correct answer is 'Released to the surroundings', indicating that the reaction gives off energy rather than absorbing or creating it.

Tags

NGSS.MS-PS3-5

Which of the following is the correct balanced equation for the combustion of methane (CH₄)?

• CH₄ + O₂ → CO₂ + H₂O

• CH₄ + 2O₂ → CO₂ + 2H₂O

• CH₄ + 2O₂ → 2CO + 2H₂O

• 2CH₄ + O₂ → 2CO₂ + H₂O

Answer explanation

The correct balanced equation for the combustion of methane is CH₄ + 2O₂ → CO₂ + 2H₂O. This shows that one molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water.

Tags

NGSS.MS-PS1-1

NGSS.MS-PS1-5

Which of the following is a balanced chemical equation for the reaction between hydrogen gas and oxygen gas to form water?

Tags

NGSS.MS-PS1-5

What is the main difference between a combustion reaction and a synthesis reaction?

• Combustion must involve oxygen, while synthesis does not.

• Synthesis produces a single product, while combustion can produce multiple products.

• Combustion releases energy, while synthesis absorbs energy.

• Synthesis involves only one reactant, while combustion requires two or more.

Which of the following is an example of a single replacement reaction?

• Synthesis

• Decomposition

• Single displacement

• Double displacement

• Synthesis

• Decomposition

• Single displacement

• Combustion

Tags

NGSS.MS-PS1-2

Which of the following is an example of a double replacement reaction?