Presentation on theme: "Building Science Champions Describe the information conveyed in a chemical equation. Apply the principle of conservation of mass to chemical reactions."— Presentation transcript:
Describe the information conveyed in a chemical equation. Apply the principle of conservation of mass to chemical reactions. Identify and describe three classes of chemical reactions.
Chemical equation Subscript Reactant Product Conservation of mass Coefficient Synthesis Decomposition Replacement
Chemical Equations are short, easy ways to show a chemical reaction by using elements’ symbols instead of words. Symbols are easy to understand.
The formula will show the ratio of elements in a compound. C 12 H 22 O 11 is the chemical formula for sugar. The letter corresponds to a particular element on the periodic table. The subscript corresponds to the element that precedes the subscript. If there is no subscript after a letter then there is one (1) of that particular element. CO 2
A chemical equation summarizes a chemical reaction. The material you begin with is the REACTANT. The completed reaction is the PRODUCT. Reactant + Reactant Product + Product = YIELDS
When there are two or more reactants they are separated by a plus sign. When there are two or more products they are separated by a plus sign. The ratio of products to reactant can change. Reactant + Reactant Product Reactant Product + Product Reactant + Reactant + Reactant Product
Regardless of the total number of reactants and products involved, all the atoms at the start of the reaction have to be present at the end of the reaction. The amount of matter involved in a chemical reaction does not change. The total mass of the reactants must equal the total mass of the product.
The law of conservation states: ▪ “Matter cannot be created nor destroyed during a chemical reaction.”
Chemical equations are short hand for chemical reactions. Subscripts go to the element before them. To the left of the yield signs are reactants and to the right are products. There can be multiple products and reactants. Matter cannot be created nor destroyed.
How do masses of the atoms in the reactants of a chemical reaction compare with the atoms in the products? The number of atoms remain equal and the total of mass is unchanged.
A chemical reaction must show the same number of each type of atom on both sides of the equation. When this happens the equation is BALANCED.
H 2 + O 2 H 2 O Does the left side equal the right side? 2 Hydrogen and 2 Oxygen on the left 2 Hydrogen and 1 Oxygen on the right Not equal. So what can be done to balance the equation?
Add a coefficient of 2 in front of the H 2 O Coefficient is the number placed in front of chemical formulas in an equation. A coefficient tells how many atoms or molecules there are. The coefficient is factored out until the next sign. H 2 + O 2 2H 2 O Left side – 2 Hydrogen and 2 Oxygen Right side – 4 hydrogen and 2 Oxygen How can we balance them out?
Place a 2 in front of the H 2 in the reactant. 2H 2 + O 2 2H 2 O Left side – 4 Hydrogen and 2 Oxygen Right side – 4 Hydrogen and 2 Oxygen We are balanced!!!!!!!!!!!!!!!!!
Left side – 1 Magnesium and 2 Oxygen Right Side – 1 Magnesium and 1 Oxygen Is the equation balanced? Now what? Add 2 in front of Magnesium in the reactant and Magnesium in the product. 2Mg + O2 2MgO Are we balanced?
C + Cl2 CCl4 C + 2 Cl2CCl4 Al2O3 Al + O2 2 Al2O34 Al + 3 O2 ***You can only change coefficients you CANNOT change subscripts. ***
There are 3 major classifications of chemical reactions: Synthesis Decomposition Replacement
When two or more substances combine to make a more complex substance the process is called synthesis. Put things together. Simple + Simple Complex More reactants than products 2 SO 2 + O 2 + 2 H 2 O2 H 2 SO 4 Sulfur dioxide + Oxygen + water yields sulfuric acid
Decomposition breaks down reactants into smaller products. Complex Simple + Simple More products than reactants 2 H2O2 2 H2O + O2 Hydrogen peroxide yields water and oxygen gas
When one element replaces another in a compound, or when 2 elements in different compound trade places, this is replacement. Reactant + Reactant Product + Product CaCO 3 + 2 HCl CaCl 2 + H 2 O 3 2 CuO + C2 Cu + CO 2
Chemical equations show chemical reactions Matter cannot be created nor destroyed Three types of chemical reactions Synthesis Decomposition Replacement
Anderson, M. et all (2012) Physical Science. McGraw-Hill: Columbus Frank, D.V et al (2001). Physical Science. Prentice Hall: New Jersey