Balancing chemical reactions: A tutorial

1. Balancing chemical reactions: A tutorial By: Jennifer Kocan & Hunter Edwards

2. What is a Chemical Reaction? • A chemical reaction is a change in which two or more substances combine to form a new substance or substances. http://dev-school.discoveryeducation.com/curriculumcenter/chemistry/glossary.html • The two or more products you begin with are called reactants. • The new substance(s) formed are called products. • For example, when the acetic acid in vinegar and baking soda (reactants) are combined, the products are bubbles of carbon dioxide gas, water, and sodium acetate. http://www.enotes.com/science-experiments-projects/chemical-properties/

3. The Law of Conservation of Mass • “A relation stating that in a chemical reaction, the mass of the products equals the mass of the reactants.” http://chemistry.about.com/library/glossary/bldef5660.htm • This means when a chemical reaction occurs, the products and reactants will have the same mass.

4. Why is it Important to Balance Chemical Reactions? • Balanced chemical equations obey the Law of Conservation of Matter and are true representations of what actually occurs in nature. http://galileo.phys.virginia.edu/education/outreach/8thgradesol/ConservMatter.htm • Remember- A chemical equation is a shorthand method for describing a chemical change. http://microship.com/resources/resourcepix/cgdb-1.jpg

5. Step 1 • To start, place reactants on the left-hand side of the equation. • Products go on the right hand side of the equation. • Remember- The law of conservation of mass states that matter is neither created or destroyed, so all the atoms in the reactants must end up somewhere among the products.

6. Example (Step 1) • Here you have an unbalanced equation. K + Br2 KBr

7. Step 2 • Count the number of atoms of each element, compound or ion in the reactants and products. http://facstaff.gpc.edu/~pgore/PhysicalScience/atom-with-electrons.gif

8. Example (Step 2) • Count the number of atoms of each element. K + Br2 KBr 1 1 1 2 *Make sure you understand that you must have 2 atoms of Bromine on the right side of the equation, since there are 2 atoms of Bromine on the left side.

9. Step 3 • Remember- numbers appearing in the formula below an element are known as subscripts. These can never be changed when balancing the equation or you will change the entire equation. http://chemistrygeek.com/balance1.htm

10. Step 4 • Balance the atoms one at a time by putting coefficients (simple, whole numbers written in front of chemical formulas) in front of the formula, so that the numbers of atoms of each element are equal on both sides of the equation. • This means that if you have atoms A2 and B2 on one side of the equation, you must have A2 and B2 on the other side (equal number of atoms). www.bcs.whfreeman.com/practiceofchemistry//cat_080/gloss.htm

11. Example (Step 4) • Balance: Two 2’s were placed in the underlined spots so the number of atoms of Bromine are equal. 2K + Br2 2KBr • 2 times K is 2 K (Two atoms of Potassium) • 2 atoms of Bromine • 2 times K and Br is two atoms of Potassium and two atoms of Bromine

12. Step 5 • Make sure all the coefficients are in the smallest possible whole number ratio (simplify). • Example: 4 and 6 are simplified to 2 and 3. • Basically all you’re doing when your balancing a chemical reaction equation is making sure that each side of the equation has the same number of atoms as the other side does.

13. Example (Step 5) • Here is the complete balanced equation. 2K + Br2 2KBr

14. Try This! • C5H12 + O2 -----> CO2 + H2O

15. Bibliography • Chemistrty Ciriculum center- http://dev-school.discoveryeducation.com/curriculumcenter/chemistry/glossary.html • Chemistry 1: Balancing Equations http://chemistrygeek.com/balance1.htmconservation • Conservation of matter and balancing equations http://galileo.phys.virginia.edu/education/outreach/8thgradesol/ConservMatter.htm • www.bcs.whfreeman.com/practiceofchemistry//cat_080/gloss.htm