Writing and Balancing Chemical Equation

Chemical Reactions and Equations

1. Chemical Reactions and Equations

2. Chemical Reaction Is the process by which a chemical change takes place. A change where a n ew substance is formed.

3. Chemical Equation Is the shorthand way of expressing chemical reaction using numbers, symbols and formula. Two Major Parts: Reactants Products

4. REACTANTS The starting materials These are the substances that changes when it is combined with another substance in a chemical reaction PRODUCTS The new substance The substances that result of the chemical reaction

5. Reactant Product

6. COEFFICIENT SUBSCRIPT is a number before the symbol or formula of a substance is the number of atoms of the element found in the substance

7. symbols used in Chemical equation Symbols Meaning + used to separate one reactant or product from one another. Can be read as “reacts with” when used in reactant , read as “and” when it is used in product. used to separate the reactants from the products read as "yields" or "produces" in an equation. (s) indicates that the substance is in the solid state.

8. symbols used in Chemical equation Symbols Meaning (l) indicates that the substance is in the liquid state. (g) indicates that the substance is in the gas state. ( aq ) indicates that the substance is dissolved in water comes from the term “aqueous” indicates that there is heat applied or needed to make the reaction proceed.

9. Sodium + Water Sodium Hydroxide + Hydrogen gas Example: +2 NaO + Reactants Symbol Products Coefficient Subscript  

10. 1. 2. C (s ) + O 2(g) CO 2(g ) + energy 3 . + Fe + Na 4. +   Mg(s) + Cl2(g) MgCl2(s) Try this:

11. Balancing Chemical Equations Law of Conservation of Mass the sum of the masses of the products is always the same as the sum of the masses of the reactants. states that mass is neither created nor destroyed in any ordinary chemical reaction.

12. Check for diatomic molecules . -are molecules composed of only two atoms, of either the same or different chemical elements. This includes , , , , , and .   Steps in Balancing Chemical Equations:

13. Steps in Balancing Chemical Equations: 2. Check whether the chemical formulas of all the reactants and products are correct . Check the total number of atoms of each element on each side of the equation. 3. A polyatomic ion appearing unchanged on both sides of the equation is counted as a single unit.

14. Steps in Balancing Chemical Equations: 4 . Balance the elements one at a time by using coefficients. Must not attempt to the balance the equation by changing the subscripts in the chemical formula of a substance.

15. Steps in Balancing Chemical Equations: 5. Check each atom or polyatomic ion to be sure that the equation is balanced.

16. Examples: If we had a container of hydrogen gas and burned this in the presence of oxygen, the two gases would reacts together, releasing energy, to form water. + + energy  

17. Step 1: Count the number of atoms of each element on each side of the equation. Element Reactants Products   H 2 2 Equal O 2 1 Not equal

18. Step 2: Pick one element in which you can balance. A ssign coefficient. 2 + 2 + energy * The whole equation is now balanced.  

19. 2. Nitrogen gas reacts with Hydrogen gas to form Ammonia. + N   Element Reactants Products   N 2 1 Not equal H 2 3 Not equal

21. 3. Zinc metal reacts with Hydrochloric Acid to form Zinc Chloride and Hydrogen gas. + +  

22. To balance the equation, put coefficient 2 before Hydrochloric Acid . + 2 +  

23. Chemical Reaction Keywords and concept: Chemical Equation Law of Conservation of Mass

24. Chemical Equation during Photosynthesis: CO 2(g)   + H 2 → C 6 H 12 O 6(s)   + O 2(g)   Exercises:

25. Exercises:   Chemical Equation when cooking in the gas stove: CH 4(g) + O 2(g) → CO 2(g) + H 2  

26. Chemical Equation in the Formation of Rust: Fe (s) + O 2(g) → Fe 2 O 3(s) Exercises:

27. Answers: 6 CO 2(g)   +6 H 2 → C 6 H 12 O 6(s)   + 6 O 2(g)   CH 4(g) + 3 O 2(g) → CO 2(g) +2 H 2 4 Fe (s) + 3 O 2(g) → 2 Fe 2 O 3(s)  

28. Directions: On a one whole sheet of paper, Answer the following questions. 1. What are the types of chemical reactions? 2 . Give at least 3 examples on each type. Assignment:

29. Davis , Raymond E. et.al.(2010). Modern Chemistry. (USA : Holl , Rinehart, Winston). de Borja , Rebecca S .(2011). C hemistry . ( Philippines: Books Atbp . Publishing Corp.) Hill , John W. (2010). Chemistry for Changing Times. (Singapore : Prentice Hall Companies). REferences :

30. Prepared by: Danica Z. Gutierrez.