High School Chemistry: Chemical Reactions - Chemical Equations - Reactants, Products, Law of Conservation of Mass

Chemical Equations & Law of Conservation of Mass: The Ultimate Study Guide

1. What This Is (In Plain English)

Chemical Equations are like recipes for chemistry. They show us what happens when different substances (called reactants) mix together to form new substances (called products). The Law of Conservation of Mass is a rule that says matter can't be created or destroyed, only rearranged.

This matters in real life because understanding chemical equations helps us make new medicines, clean up pollution, and even create new materials for our favorite gadgets. Without this knowledge, we wouldn't have many of the amazing technologies we use every day.

2. Key Ideas & Definitions

• Chemical Equation: A recipe that shows reactants turning into products.
  • Definition: A chemical equation is a way to write down what happens when substances mix together.
  • Example: H2 + O2-H2O (hydrogen and oxygen mix to form water)
• Reactants: The substances that mix together in a chemical equation.
  • Definition: Reactants are the ingredients that go into a chemical reaction.
  • Example: The reactants in the previous example are hydrogen (H2) and oxygen (O2)
• Products: The new substances formed in a chemical equation.
  • Definition: Products are the result of a chemical reaction.
  • Example: The product in the previous example is water (H2O)
• Law of Conservation of Mass: A rule that says matter can't be created or destroyed, only rearranged.
  • Definition: The Law of Conservation of Mass states that the total amount of matter before a reaction is equal to the total amount of matter after the reaction.
  • Example: If you have 10 grams of hydrogen and 10 grams of oxygen, you'll have 20 grams of water (not 30 grams!)
• Balanced Equation: A chemical equation where the number of atoms of each element is the same on both sides.
  • Definition: A balanced equation is a chemical equation where the reactants and products have the same number of atoms of each element.
  • Example: 2H2 + O2-2H2O (this equation is balanced because there are 2 hydrogen atoms on both sides)
• Mole: A unit of measurement that represents 6.022 x 10^23 particles (atoms or molecules).
  • Definition: A mole is a way to measure the amount of a substance.
  • Example: 1 mole of hydrogen gas contains 6.022 x 10^23 hydrogen molecules
• Coefficient: A number that tells us how many molecules of a substance are involved in a chemical reaction.
  • Definition: A coefficient is a number that tells us how many molecules of a substance are involved in a chemical reaction.
  • Example: In the equation 2H2 + O2-2H2O, the coefficient 2 tells us that there are 2 molecules of hydrogen gas involved in the reaction

3. How To Do It (Step-by-Step)

Step 1: Write the Unbalanced Equation

• Start by writing the reactants and products in a chemical equation.
• Use the correct chemical formulas for each substance.
• Example: H2 + O-H2O

Step 2: Count the Atoms

• Count the number of atoms of each element on both sides of the equation.
• Make sure the number of atoms of each element is the same on both sides.
• Example: On the left side, there is 1 hydrogen atom and 1 oxygen atom. On the right side, there is 2 hydrogen atoms and 1 oxygen atom.

Step 3: Add Coefficients

• Add coefficients to the reactants and products to balance the equation.
• Make sure the number of atoms of each element is the same on both sides.
• Example: To balance the equation, we can add a coefficient of 2 to the reactants: 2H2 + O2-2H2O

Step 4: Check the Equation

• Check the equation to make sure it is balanced.
• Make sure the number of atoms of each element is the same on both sides.
• Example: The equation 2H2 + O2-2H2O is balanced because there are 2 hydrogen atoms and 1 oxygen atom on both sides.

Step 5: Write the Balanced Equation

• Write the balanced equation in the correct format.
• Make sure the coefficients are included.
• Example: 2H2 + O2-2H2O

4. Watch Out! (Common Mistakes)

• Mistake: Forgetting to balance the equation.
  • Fix: Make sure to count the atoms on both sides of the equation and add coefficients as needed.
  • Example: If you forget to balance the equation, you might end up with an unbalanced equation like H2 + O-H2O.
• Mistake: Not using the correct chemical formulas.
  • Fix: Make sure to use the correct chemical formulas for each substance.
  • Example: If you use the wrong chemical formula, you might end up with an equation like H2 + O-H2O (instead of H2 + O2-H2O).
• Mistake: Not checking the equation for balance.
  • Fix: Make sure to check the equation to make sure it is balanced.
  • Example: If you don't check the equation, you might end up with an unbalanced equation like 2H2 + O-2H2O.

5. Practice Problems

Problem 1:

Write a balanced equation for the reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O).

Solution:

• Start by writing the unbalanced equation: H2 + O2-H2O
• Count the atoms: On the left side, there is 1 hydrogen atom and 1 oxygen atom. On the right side, there is 2 hydrogen atoms and 1 oxygen atom.
• Add coefficients: To balance the equation, we can add a coefficient of 2 to the reactants: 2H2 + O2-2H2O
• Check the equation: The equation is balanced because there are 2 hydrogen atoms and 1 oxygen atom on both sides.

Problem 2:

Write a balanced equation for the reaction between carbon dioxide (CO2) and water (H2O) to form carbonic acid (H2CO3).

Solution:

• Start by writing the unbalanced equation: CO2 + H2O-H2CO3
• Count the atoms: On the left side, there is 1 carbon atom, 2 hydrogen atoms, and 2 oxygen atoms. On the right side, there is 1 carbon atom, 2 hydrogen atoms, and 3 oxygen atoms.
• Add coefficients: To balance the equation, we can add a coefficient of 2 to the reactants: 2CO2 + 2H2O-2H2CO3
• Check the equation: The equation is balanced because there are 2 carbon atoms, 4 hydrogen atoms, and 4 oxygen atoms on both sides.

6. Cram Sheet

• Chemical Equation: A recipe that shows reactants turning into products.
• Reactants: The substances that mix together in a chemical equation.
• Products: The new substances formed in a chemical equation.
• Law of Conservation of Mass: A rule that says matter can't be created or destroyed, only rearranged.
• Balanced Equation: A chemical equation where the number of atoms of each element is the same on both sides.
• Mole: A unit of measurement that represents 6.022 x 10^23 particles (atoms or molecules).
• Coefficient: A number that tells us how many molecules of a substance are involved in a chemical reaction.
• Mass stays the same during a phase change; energy is what changes.
• A mole of any substance contains 6.022 x 10^23 particles.
• Coefficients tell us how many molecules of a substance are involved in a chemical reaction.

7. Where to Learn More

• YouTube: Check out the Amoeba Sisters channel for fun and engaging chemistry videos.
• PhET Simulations: Try out the PhET simulation for chemical reactions to see how different substances interact.
• School-Friendly Website: Visit the Chemistry LibreTexts website for a comprehensive and easy-to-understand guide to chemistry.