Monday, November 1

We started class today by turning in our homework from the Chemthink assignment. We reviewed what we learned on Friday about chemical reactions. Here are some facts about chemical reactions:

• Always rearrangement of atoms



• Breaks bonds and forms new bonds



• Reactants (starting materials) turned into products (ending materials)



• Conservation of mass (atoms are neither created nor destroyed)



• Conservation of charge (protons and electrons are neither created nor destroyed)



• Represented symbollically by chemical equations

We then practiced what we learned by doing page 1 in the unit packet.

Question 1 involved writing the formula of reactants and products based on a picture. We talked about turning the visual into words, so it would be 1 molecule of methane gas reacts with 2 molecules of oxygen to create 1 molecule of carbon dioxide and 2 molecules of water. We then were able to write the formula for that. The arrow between the reactants and products represent that the reactants turned into the product. In question 2, we had to use our unit 1 skills to count the number of atoms in different chemical reaction formulas. The numbers should be equal in both sides of the equation, which means that the atoms were conserved. For questions 3 and 4 we had to count the number of each atom on the reactant and product side of a given equation. If there are the same number of atoms on both sides, that means it is a balanced equation.

We then learned about balancing chemical equations. Here are some important things to remember while balancing a chemical equation.

• Add coefficients in front of formulas. (Do NOT change formulas' subscripts and supersubscripts)


• Trial and error process

- do one element at a time; pick the element that is present in one location on reactant and product side

- use whole number coefficients; if a coefficient comes out to be a half number, double them all

We practiced balancing equations by doing page 2 in the packet.

With question 5, we started with balancing N. Since there were 2 N molecules on left, but only 1 on the right, we added a coefficient of 2 in front of NH3 on the product side. That caused there to be 6 H molecules on the product side. We added the coefficient 3 in front of H2 so that there would also be 6 molecules of H on the reactant side. The balanced equation was now N2+3H2 ---> 2NH3. To make sure this is correct, you could count the number of each atom on each side and make sure they are equal. Mr. H reminded us to make sure that when balancing equations, you always want the lowest possible set of whole numbers.

We were assigned our homework, which is to read page 5-6 in the packet and 60-61 in the textbook. These are about classifying reactions.

We ended class with a demonstration of the solid zinc reacting with the aqueaous hydrochloric acid. This created hydrogen gas and zinc chloride. The chemcial formula for it looked like this:

Zn(s)+2HCl (aq) ---> H2 (g) + ZnCl2 (aq)

The signs that this was a chemical reaction were that a gas formed and the test tube was warm.

Here is a video of the reaction of zinc with hydorchloric acid.

http://www.youtube.com/watch?v=CfrsElKZaLU&feature=related