TERM 1 - WEEK 6
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Chemical reactions involve the breaking and formation of chemical bonds, resulting in the rearrangement of atoms to produce new substances. Although the substances change, the total number of atoms remains the same. This principle, known as the law of conservation of mass, states that matter cannot be created or destroyed during a chemical reaction. By applying this principle, chemical equations can be balanced to show that the total mass of the reactants is equal to the total mass of the products.
DAY 1: Explain the principle of conservation of mass and describe how atoms are neither created nor destroyed during chemical reactions.
The principle of conservation of mass states that matter cannot be created or destroyed during a chemical reaction. Instead, the atoms in the reactants are rearranged to form new substances called products. The same types and numbers of atoms that are present before the reaction must also be present after the reaction. For example, in 2H₂ + O₂ → 2H₂O, the hydrogen and oxygen atoms are rearranged to form water, but no hydrogen or oxygen atoms are lost or created. This is why chemical equations must be balanced—the number of atoms of each element must be equal on both sides of the equation.
DAY 2: Distinguish between balanced and unbalanced chemical equations by
counting atoms on both sides.
To distinguish between balanced and unbalanced chemical equations, count the atoms of each element on the reactant side and compare them with the atoms on the product side. A balanced equation has the same number of atoms of every element on both sides, while an unbalanced equation has different numbers of one or more elements.
DAY 3: Balance simple chemical equations using coefficients while applying conservation of mass
To balance a simple chemical equation, first write the skeleton equation showing the reactants and products. Next, count the number of atoms of each element on both sides of the equation. If the numbers are not equal, place coefficients in front of the chemical formulas to make the number of atoms equal. Balance one element at a time, usually starting with an element that appears in only one reactant and one product. After adding each coefficient, recount all the atoms to check the changes. Continue adjusting the coefficients until the number of atoms of every element is the same on both sides. Finally, make sure the coefficients are in the smallest whole-number ratio. For example, H₂ + O₂ → H₂O becomes 2H₂ + O₂ → 2H₂O, with four hydrogen atoms and two oxygen atoms on both sides. This demonstrates the Law of Conservation of Mass because the atoms are neither created nor destroyed; they are simply rearranged.
Note: Complete the ChemBalance Activity to check your understanding.
DAY 4: Apply balancing strategies to more complex equations and explain their reasoning.
The ABCD (Algebraic) Method is a systematic way of balancing chemical equations by using variables and algebraic equations to determine the correct coefficients. First, assign a variable such as A, B, C, or D to each coefficient in the chemical equation. Next, build an algebraic equation for each element by comparing the number of atoms on the reactant and product sides. Then, calculate the values of the variables by choosing a convenient value for one variable and solving for the others. Finally, double-check the equation by substituting the values as coefficients and counting the atoms of each element on both sides. For example, in AFe + BO₂ → CFe₂O₃, the iron atoms give A = 2C, while the oxygen atoms give 2B = 3C. If C = 2, then A = 4 and B = 3, giving the balanced equation 4Fe + 3O₂ → 2Fe₂O₃. This method applies the Law of Conservation of Mass because it ensures that the same number of atoms of each element is present on both sides.
DAY 5: Relate balanced equations to real-world chemical processes and demonstrate mastery through problem solving.
Balanced chemical equations are useful in describing real-world chemical processes because they show the exact ratio of substances that react and the products that are formed. For example, combustion of methane can be represented by CH₄ + 2O₂ → CO₂ + 2H₂O. This equation shows that one molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water. In real life, this reaction occurs when natural gas burns for cooking or heating. By solving problems involving balanced equations, learners can determine the amounts of reactants needed or products produced while applying the Law of Conservation of Mass.
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