Chemical Reaction 10 Example of Simple Chemical Equation

LEARNING OBJECTIVES

Define chemical reaction.
Use a balanced chemical equation to represent a chemical reaction.
20 Key Terminologies in Chemical Equations and Balancing
10 Example of simple chemical equation Chemical Reaction 10 Example of Simple Chemical Equation

Definition Chemical Reaction

Chemical Reaction 10 Example of Simple Chemical Equation

Water (H₂O) is composed of hydrogen and oxygen. Let us imagine a process in which we take some elemental hydrogen (H₂) and elemental oxygen (O₂) and let them react to make water.

The statement simply means Hydrogen and oxygen react together to produce water, this can be represent in a way or represent in that process, which is called a chemical reaction.

To simplify the writing of this reactions, we use formulas instead of names when we describe a reaction. We can also use symbols to represent other words in the reaction. A plus sign connects the initial substances (and final substances, if there is more than one), and an arrow (→) represents the chemical change:

H₂ + O₂ → H₂O. This a chemical reaction for water in chemical equation.

This statement is one example of a chemical equation, an abbreviated way of using symbols to represent a chemical change. The substances on the left side of the arrow are called reactants, and the substances on the right side of the arrow are called products. It is not uncommon to include a phase label with each formula—(s) for solid, (ℓ) for liquid, (g) for gas, and (aq) for a substance dissolved in water, also known as an aqueous solution. If we included phase labels for the reactants and products, under normal environmental conditions, the reaction would be as follows:

H₂(g) + O₂(g) → H₂O(ℓ)

Chemical equations can also be used to describe physical changes.

Use a balanced chemical equation to represent a chemical reaction.

EXAMPLE 1

Is each chemical equation balanced?

2Na(s) + O₂(g) → 2Na₂O(s)
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(ℓ)
AgNO₃(aq) + 2KCl(aq) → AgCl(s) + KNO₃(aq)

SOLUTION

1. By counting, we find two sodium atoms and two oxygen atoms in the reactants and four sodium atoms and two oxygen atoms in the products. This equation is not balanced.

The reactants have one carbon atom, four hydrogen atoms, and four oxygen atoms. The products have one carbon atom, four hydrogen atoms, and four oxygen atoms. This equation is balanced.

3. The reactants have one silver atom, one nitrogen atom, three oxygen atoms, two potassium atoms, and two chlorine atoms. The products have one silver atom, one chlorine atom, one potassium atom, one nitrogen atom, and three oxygen atoms. Because there are different numbers of chlorine and potassium atoms, this equation is not balanced.

SKILL-BUILDING EXERCISE

Is each chemical equation balanced?

2Hg(ℓ) + O₂(g) → Hg₂O₂(s)
C₂H₄(g) + 2O₂(g) → 2CO₂(g) + 2H₂O(ℓ)
Mg(NO₃)₂(s) + 2Li(s) → Mg(s) + 2LiNO₃(s)

How does one balance a chemical equation, starting with the correct formulas of the reactants and products? Basically, a back-and-forth approach is adopted, counting the number of atoms of one element on one side, checking the number of atoms of that element on the other side, and changing a coefficient if necessary. Then check another element, going back and forth from one side of the equation to another, until each element has the same number of atoms on both sides of the arrow. In many cases, it does not matter which element is balanced first and which is balanced last, as long as all elements have the same number of atoms on each side of the equation.

For example, to balance the equation

CH₄ + Cl₂ → CCl₄ + HCl

we might choose to count the carbon atoms first, finding that both sides are balanced with one carbon atom. The reactant side has four hydrogen atoms, so the product side must also have four hydrogen atoms. We fix this by putting a 4 in front of the HCl:

CH₄ + Cl₂ → CCl₄ + 4HCl

Now each side has four hydrogen atoms. The product side has a total of eight chlorine atoms (four from the CCl₄ and four from the four molecules of HCl), so we need eight chlorine atoms as reactants. Because elemental chlorine is a diatomic molecule, we need four chlorine molecules to get a total of eight chlorine atoms. We add another 4 in front of the Cl₂ reactant:

CH₄ + 4Cl₂ → CCl₄ + 4HCl

Now we check: each side has one carbon atom, four hydrogen atoms, and eight chlorine atoms. The chemical equation is balanced.

20 Key Terminologies in Chemical Equations and Balancing

Chemical Equation

Definition: A symbolic representation of a chemical reaction, showing reactants and products with their respective quantities. Example:
Coefficient: The coefficient is the number placed in front of a chemical formula to indicate how many molecules or moles of that substance are involved in the reaction. Example: In he coefficients are 2 for H2 and
Subscript: The subscript is the small number written after an element’s symbol within a chemical formula, indicating the number of atoms of that element in a single molecule of the substance. Example: In he subscript “2” indicates two hydrogen atoms.
Reactants
- Definition: Substances that undergo change in a chemical reaction.
- Example: In

Products
- Definition: Substances formed as a result of a chemical reaction.
Example: Hydrogen () is the product in the reaction above.
Law of Conservation of Mass
- Definition: Mass is neither created nor destroyed in a chemical reaction; the mass of reactants equals the mass of products.
- Implication: Chemical equations must be balanced to reflect this law.
Balancing a Chemical Equation
- Definition: Adjusting coefficients to ensure the number of atoms for each element is the same on both sides of the equation.
- Purpose: To satisfy the Law of Conservation of Mass.
Molecule
- Definition: The smallest unit of a chemical compound that can exist; composed of two or more atoms bonded together. Example: is a water molecule.
Atom
- Definition: The smallest unit of an element that retains the properties of that element.
- Example: A hydrogen atom ( $H$ ).
Element
- Definition: A substance that cannot be broken down into simpler substances by chemical means. Example: Oxygen ( $O$ ), Hydrogen ().
Compound
- Definition: A substance formed when two or more different elements are chemically bonded together.
- Example: Water (, carbon dioxide ( $CO_{2}$ ).

Coefficient Adjustment
- Definition: Changing the coefficients to balance the number of atoms for each element.
- Example: Changing
Mole
- Definition: A unit representing $6.022×10^23$ particles (atoms, molecules, etc.) of a substance.
- Usage: Used to express amounts of reactants and products in equations.
Stoichiometry
- Definition: The calculation of reactants and products in chemical reactions using balanced equations.
- Application: Determining how much product is formed from given reactants.
State Symbols
- Definition: Indicators of the physical state of each substance in a chemical equation.
- Common Symbols:
  - $(s)$ : Solid
  - State Symbols
    - Definition: Indicators of the physical state of each substance in a chemical equation.
    - Common Symbols:
      - : Solid
      - : Liquid
      - : Gas
      - : Aqueous solution
  - Net Ionic Equation. Definition: A chemical equation that shows only the species that actually participate in the reaction, excluding spectator ions.
    - $(l)$ : Liquid
    - : Gas
    - : Aqueous solution
Net Ionic Equation
- Definition: A chemical equation that shows only the species that actually participate in the reaction, excluding spectator ions.
- Net Ionic Equation
  - Definition: A chemical equation that shows only the species that actually participate in the reaction, excluding spectator ions.
  - Example: For the reaction , the net ionic equation is $(a q) \to AgCl (s).$