Unit 2 Section C Conservation
C.1 Keeping Track of Atoms In some reactions, matter seems to appear and others matter seems to disappear. Matter seems to disappear in our daily lives. Gas in tank, food we eat, etc.
Basically, “using things up” means changing materials chemically, not destroying them. Law of Conservation of Matter- matter is not created nor destroyed
Recall, that reactants are on the left of a chemical equation and products are on the right. C + O2 CO2 Note that the numbers of carbon and oxygen are the same on both sides.
Cu + O2 CuO Note that the number of Cu and O are not equal. To balance the equation, coefficients need to be used to get the same # on both sides 2Cu + O2 2CuO
Formula Unit- refers to the smallest unit of an ionic compound. Molecules refer to covalently bonded compounds.
C.2 Nature’s Conservation: Balanced Chemical Equations Conservation works because atoms are indestructible. To balance equation, start by doing an atom inventory. That is, are the numbers of each atom equal on both sides. See page 131-132.
Additional Rules If polyatomic ions, such as NO3 and CO2, treat as a unit. Balance H and O last.
C.3 Atom, Molecule, and Ion Inventory It is not very useful to talk about single atom or formula units in an equation. Chemists use a counting unit called the mole You are familiar with a “pair” or “dozen”
One mole equals 602000000000000000000000 of anything. Or 6.02 x 1023 This is called Avogadro’s number
See the first paragraph on page 136. Molar mass – mass of one mole of any substance. Equal to the mass on the periodic table
In a balanced equation, the coefficient equals the number of molecules but also the moles of the same substances 2Cu + O2 2CuO This means 2 moles of copper reacts with 1 mole of oxygen to produce copper (II) oxide
C.4 Composition of Materials One helpful property of matter is Percent composition- percent by mass of a material in a substance Helpful to determine what elements to mine from what ores.
What is the percent composition of Cu in Cu(NO3)2?