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Presentation on theme: "D ESCRIBING C HEMICAL R EACTIONS Chapter 6 Section 2."— Presentation transcript:


2 WHAT ARE CHEMICAL EQUATIONS? Is a short, easy way to show a chemical reaction, using symbols instead of words.

3 Uses chemical formulas with subscripts and coefficients to summarize a reaction

4 A formula is a combination of symbols that represents elements in the compound

5 The substances at the left of the equation are called reactants, when the reaction is complete, on the right you have products.

6 If you have two or more reactants or products they are separated by a + sign Reactant 1 + reactant 2 ----> Product 1 + product 2

7 C ONVERSION OF MASS During a chemical reaction, matter is neither created nor destroyed, it just changes form.

8 All the atoms present at the start of the reaction are present at the end

9 The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products

10 O PEN AND CLOSED SYSTEMS Open: matter can enter from or escape to the surroundings. Burning match

11 Closed: matter is not allowed to enter or leave the system Eg: reaction is sealed in a plastic bag

12 B ALANCING C HEMICAL E QUATIONS To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation

13 4 Step process Step 1: Write the equation : Reactants on the Left, products on the right ___H ₂ + ___O ₂ ----> ____H ₂ 0 

14 Step 2: Count the number of atoms of each element on each side of the equation 2 hydrogen, 2 oxygen on the react side, 1 oxygen and 2 hydrogen on the product side. IF THE ATOMS DO NOT EQUAL GO TO STEP 3

15 Step 3: Use coefficients to balance atoms A coefficient is a number placed in front of a chemical formula. It is multiplied by the subscript to get the new number of atoms Always check both sides when using a coefficient

16 Step 4: Check your work

17 C LASSIFYING C HEMICAL REACTIONS Synthesis: when 2 or more elements or compounds combine to make a more complex substance 2H ₂ + O ₂ ---> 2 H ₂ O

18 Decomposition: Breaks down compounds into simpler products 2H ₂ O ₂ ----> 2H ₂ O + O ₂

19 Replacement: When one element replaces another element in a compound or when 2 elements in different compounds trade places 2CuO + C ----> 4 Cu + CO ₂ FeS + 2 HCl ----> FeCl ₂ + H ₂ S

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