Molecules vs Compounds Molecules are two or more atoms bonded together…but compounds must have two different elements – Ex- O2, NaCl, etc. REMEMBER: – Not all molecules are compounds, but all compounds are molecules…explain
Chemical reactions continued –Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken What do we call those “outermost parts”??? Valence electrons
Symbols represent elements Formulas represent the molecules Chemical equations represent the reaction
Law of conservation of matter “ mass is neither created nor destroyed in any ordinary chemical reaction. “ Or more simply, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).
Balancing Equations To follow the law of conservation of mass, any equation must be BALANCED (Mass of reactants must equal the mass of the products)
BALANCING EQUATIONS not –When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the … subscripts. Changing the subscripts changes the compound. –H 2 O is very different that H 2 O 2 –(Water vs Hydrogen Peroxide!)
Subscripts tell you how many atoms of each element you have Coefficients tell you how many of each molecule you have
Ex: 4 Al + 3 O 2 2Al 2 O 3 This equation means : “4 Al atoms + 3 O 2 molecules produces 2 molecules of Al 2 O 3 ”
Steps to Balancing Chemical Equations 1. Write out the equation leaving room to add coefficients. Ex- Na 3 PO 4 + Fe 2 O 3 Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O 3 Na 2 O + FePO 4
Step 2: Record how many atoms of each element 2. Find the number of atoms for each element on each side. – YOU MUST COMBINE ALL of the same element together… – ex Na 3 PO 4 + Fe 2 O 3 Na 2 O + FePO 4 » Na- 3Na-2 » P-1P-1 » O- 7Fe- 1 » Fe-2O-5 HINT- write them in the same order on both sides so that it is easier to compare them
STEP THREE Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.
2 Na 3 PO 4 +___ Fe 2 O 3 3 Na 2 O + 2 FePO 4 » Na- 3 6Na-2 6 » P-12P-1 2 » Fe- 2Fe- 1 2 » O- 711O-5 9 11
Step 4… 4. Check your answer to see if: –The numbers of atoms on both sides of the equation are now balanced. –The coefficients are in the lowest possible whole number ratios. (reduced)
Some Helpful Hints for balancing equations: Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last. IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element)
Let’s try a few 1. ___ C 3 H 8 + ___ O 2 ____ CO 2 + ___ H 2 O
Ready for another? 2. _____B 4 H 10 +___O 2 __B 2 O 3 + ____H 2 O
Balancing Equations when given the name (not the formula) Use “reacts with” and “produces” or “yields” Ex- Hydrogen reacts with Oxygen to produce dihydrogen monoxide. Be able to write the chemical equation from the word equation or vice versa!
Let’s try a few 1.___ C 3 H 8 + ___ O 2 ____ CO 2 + ___ H 2 O Tricarbon octohydride reacts with oxygen to produce carbon dioxide and dihydrogen monoxide
Ready for another? 2. _____B 4 H 10 +___O 2 __B 2 O 3 + ____H 2 O Tetraboron decahydride reacts with oxygen to produce diboron trioxide and dihydrogen monoxide
Ready for another? 3. _____MgCl 2 +___NaF __MgF 2 + ____NaCl Magnesium chloride reacts with sodium fluoride to produce magnesium fluoride and sodium chloride