Unit 4, Lessons 1 and 2

Lesson 1:

A chemical equation illustrates what happens, and what substances are involved, in chemical reactions. They are a way that scientists keep track of matter. Most chemical equations write out the substances involved in a reaction in the same way that mathematicians do. One one side of the equation, two reactants are added together, and on the other side, addition is also used. A further example is:

2HCl(aq) + Cr(s) --> CrCl2(aq) + H2(g)

Which is read aloud as:

"An aqueous solution of hydrochloric acid reacts with solid chromium to produce an aqueous chromium chloride solution and hydrogen gas."

Not everything about a chemical reaction can be observed through the senses, which is why these equations exist! Two substances, like hydrochloric acid and water, water and salt water, things like that...can all be clear, and therefore we might not be able to tell the difference between them. 

Problems:

1.) What is the difference between  reactant and a product? A reactant is what is combined with another substance (another reactant) in a chemical equation. The product is what the reactants make, and usually marks the end of the reaction.

6.) Describe at least three types of effects that a toxic substance can have on the body. If ingested, a toxin can cause severe nausea, diarrhea, blood acidosis, or possibly even kidney stones. If taken in through the nose, perhaps even the skin, hallucinations can occur.

Lesson 2:

In addition to specifying which substances are what, chemical equations also clue us in to possible phase changes. From them, we can predict what we might observe during a reaction. For example, the equation in Lesson 1 tells us that an aqueous solution and a solid come together to create a liquid with a solid precipitate (another aqueous solution) and a gas. There will probably be some bubbling, some evaporation, to produce the hydrogen. If we have bubbles rising, we might need some heat, so a temperature change could also be observed.

Problems:

2.) Use chemical equations to describe the difference between sugar melting and sugar decomposing. The formula for sugar is C12H22O11. The melting process of sugar is a physical change, because sugar molecules don't have to change their identity. The chemical equation or melting sugar is C12H22O11(s) --> C12H22O11(l), and vice versa as sugar sets afterwards. Decomposing sugar, however, involves the splitting of sugar molecules. They break apart, as the word suggests. The chemical equation for decomposing sugar is C12H22O11(s) --> 12C(s) + 11H20(g).

4. Write a chemical equation for these reaction descriptions:

A.) Solid sodium chloride dissolves in water. NaCl(s) + H2O(l) --> NaCl(aq)

B.) Solid magnesium sulfide is heated to produce solid magnesium and sulfur gas. MgS(s) --> Mg(s) + S(g)

C.) Solid titanium is heated in oxygen gas to produce titanium dioxide. Ti(s) + O2(g) --> TiO2(s)