Balancing Chemical Equations notes for p. 8-10

Transcription

1 Balancing Chemical Equations notes for p. 8-10

2 Balanced Equation Atoms can t be created or destroyed Law of Conservation of Mass All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation (reactant and product sides).

3 Counting Atoms H + H Reactants product Subscript: (numbers below) indicates how many atoms of an element. Coefficient (numbers in front) Indicates how many molecules/moles of a compound (multiplies the number of atoms of each element in the compound)

4 Chemical Formula Counting up Atoms

5 Let s Practice NH 3 atoms of Nitrogen atoms of Hydrogen molecules/moles of NH 3 NaCl atoms of Sodium atoms of Chlorine molecule/moles of NaCl

6 Practice NH 3 1 atoms of Nitrogen 3 atoms of Hydrogen 1 molecules/moles of NH 3 NaCl 1 atoms of Sodium 1 atoms of Chlorine 1 molecule/moles of NaCl

7 Practice Again 8NaCl atoms of Sodium atoms of Chlorine molecule/moles of NaCl 3NH 3 atoms of Nitrogen atoms of Hydrogen molecule/moles of NH 3 Ca(N 3 ) atoms of Calcium atoms of Nitrogen atoms of xygen molecule/moles of Ca(N 3 )

8 8NaCl Practice Again 8 atoms of Sodium 8 atoms of Chlorine 8 molecule/moles of NaCl 3NH 3 3 atoms of Nitrogen 9 atoms of Hydrogen 3_ molecules/moles of NH 3 Ca(N 3 ) 1 atoms of Calcium atoms of Nitrogen 6 atoms of xygen 1 molecule/moles of Ca(N 3 ) What if there is a coefficient of in front of Ca(N 3 )?

9 S + 3H atoms of Sulfur More Practice atoms of Hydrogen atoms of xygen molecule/moles of S molecules of H

10 S + 3H More Practice 1 atoms of Sulfur 6 atoms of Hydrogen 5 atoms of xygen 1 molecule/moles of S 3 molecules of H

11 Let s Step It Up a Little NH 4 N 3 + 3H S atoms of Nitrogen atoms of Hydrogen atoms of xygen atoms of Sulfur molecule/moles of NH 4 N 3 molecule/moles of H S

12 Let s Step It Up a Little NH 4 N 3 + 3H S 4 atoms of Nitrogen 14 atoms of Hydrogen 6 atoms of xygen 3 atoms of Sulfur molecule/moles of NH 4 N 3 3 molecule/moles of H S

13 You Must Be Joking! Na C 3 + 3C + 4NaCl + Mg(N 3 ) atoms of Sodium atoms of Carbon atoms of xygen atoms of Chlorine atoms of Nitrogen atoms of Magnesium molecules/moles of Na C 3 molecule/moles of C molecule/moles of NaCl molecule/moles of Mg(N 3 )

14 You Must Be Joking! Na C 3 + 3C + 4NaCl + Mg(N 3 ) 8 atoms of Sodium 5 atoms of Carbon 18 atoms of xygen 4 atoms of Chlorine atoms of Nitrogen 1 atom of Magnesium molecules/moles of Na C 3 3 molecule/moles of C 4 molecule/moles of NaCl 1 molecule/moles of Mg(N 3 )

15 C + C Shows the reaction to form carbon dioxide C + C This equation is already balanced What if it isn t already?

16 C + C Shows the reaction to form carbon monoxide C + C We need one more oxygen in the products. Can t change the formula, because it describes what is produced. Remember, oxygen is a diatomic molecule.

17 C + C C The other xygen must be used to make another C But where did the other C come from?

18 C C + C C Must have started with two C C + C

19 Rules for balancing Write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements (make them same amount on reactant and product sides) one at a time by adding coefficients (the numbers in front). Check to make sure it is balanced.

20 Never! Change a subscript to balance an equation. If you change the formula you are describing a different reaction. H is a different compound than H Never put a coefficient in the middle of a formula NaCl is okay, NaCl is not.

21 Example H + H Make a table to keep track of where you are at

22 Example H + H R H P 1 Need twice as much in the product

23 Example H + H R H P 1 Changes the

24 Example H + H R P H 1 Also changes the H

25 Example H + H R P H 4 1 Need twice as much H in the reactant

26 Example H + H R P H 4 1 Recount

27 Example H + H R P 4 H 4 1 The equation is balanced, has the same number of each kind of atom on both sides

28 Example H + H R P 4 H 4 1 Not this This is the answer

29 Examples CH 4 + C + H AgN 3 + Cu Cu(N 3 ) + Ag Mg + N Mg 3 N P + P 4 10 Na + H H + NaH

30 Examples CH 4 + C + H AgN 3 + Cu Cu(N 3 ) + Ag 3Mg + N Mg 3 N 4P + 5 P 4 10 Na + H H + NaH