Unit 4, Lessons 5 and 6

Lesson 5:

For a chemical equation to demonstrate a chemical reaction that's actually possible, it must represent a true mathematical relationship between products and reactants. Simply put, there must be an equal number of atoms on each side of the equation. This ties into the law of conservation of mass and that of matter. "True mathematical relationship" is synonymous with "balanced." You can balance an equation by adding coefficients, and coefficients only. Not the little numbers at the bottom, subscripts. Coefficients let scientists know how many molecules or single atoms of a substance there are in an equation. They're measuring tools!

Problems:

1.) Why do chemical equations need to be balanced? Chemical equations that aren't balanced make for reactions that either don't work properly or don't happen at all. When they are balanced, the reactions are easier to control, and typically give one their desired result!

2.) How are subscripts and coefficients different from one another in chemical equations? If there is a substance with an atom that has a subscript, that tiny number only applies to the element that it hugs. The coefficients, however, must be distributed, and thus multiply everything in a compound.

Lesson 6:

Chemical reactions can be classified to a degree further than just "chemical" or "physical". When one looks at a chemical equation, they might notice that some elements or molecules switch places in the products. The new types of classification we learned in Lesson 6 are as follows:

Combination: A + B --> AB

Single exchange: A + BC --> AC +B

Double exchange: AB + CD --> AD + CB

Decomposition: AB --> A + B

In combination reactions, reactants combine and form one single product.

In single exchange reactions, reactants combine and one factor from either the first compound or the second switches to create two different products.

In double exchange reactions, two factors, one from both compounds, switch places and make two different products.

In decomposition reactions, an already existing substance breaks apart into its components.

Problems: 

4.) List four molecules and four ionic compounds from the reactions in exercise 3.

                    MOLECULES                                     IONIC COMPOUNDS

                           HNO3(aq)                                                       MgBr2(s)

                             Cl2(g)                                                            NaOH(aq)

                           C2H4(g)                                                          NaNO3(aq)

                              Br2(s)                                                           MgCl2(s)

6.) Solid lithium reacts with aqueous hydrochloric acid to produce hydrogen gas and aqueous lithium chloride: 2Li(s) + 2HCl(aq) --> H2(g) + 2LiCl

^ There are 2 lithium atoms, 2 hydrogen atoms, and 2 chlorine atoms on both sides