Balancing Chemical Equations

Obeying the Law of Conservation of Matter/Mass

BCl3 + P4 + H2 BP + HCl

• Make a T-chart with reactants on the left & products on the right

• Tally the number of each atom of each element: R_ P

B 1 1Cl 3 1P 4 1H 2 1

BCl3 + P4 + H2 BP + HCl• Notice on the T-chart a noticeable difference

between Reactant & Product and start there• I would choose P. Write the coefficient 4 in

front of BP so that the P’s balance. BCl3 + P4 + H2 4BP + HCl• Recalculate the T-chart. Note that now R’s

Boron has 1, but P’s Boron now has 4. Place a coefficient of 4 in front of BCl3

4BCl3 + P4 + H2 4BP + HCl

#1] 4BCl3 + P4 + H2 4BP + HCl

• Update T-chart. R_ PB 4 4Cl 12 1 12P 4 4H 2 1 12

Note Cl’s lack of balance. Place a 12 before HCl. 4BCl3 + P4 + H2 4BP + 12HCl

Note new imbalance of H now. Fix this by adding 6 before H2.

4BCl3 + P4 + 6H2 4BP + 12HCl DONE!!!

C2H2Cl4 + Ca(OH)2 C2HCl3 + CaCl2 + H2O

• Fix T-chart. C H Cl Ca O

R: 2 4 4 1 2P: 2 3 5 1 1Notice that R’s Cl is 4 & therefore P’s Cl must be a

multiple of 4. The Cl in C2HCl3 is an odd #. Begin by adding a coefficient of 2 to create an even number of Cl.

C2H2Cl4 + Ca(OH)2 2C2HCl3 + CaCl2 + H2O

Recalculate the T-chart.

#2] C2H2Cl4 + Ca(OH)2 2C2HCl3 + CaCl2 + H2O

C H Cl Ca OR: 2 4 4 1 2P: 4 4 8 1 1Right away you can see that to balance C & Cl, we

need to write a coefficient of 2 before the 1st cpd.2C2H2Cl4 + Ca(OH)2 2C2HCl3 + CaCl2 + H2O

C H Cl Ca OR: 4 6 8 1 2P: 4 4 6 8 1 1 2 To fix O, add 2 before H2O. DONE!

#3] (NH4)2Cr2O7 N2 + Cr2O3 + H2O

• Fix T-chart.• N H Cr O

R: 2 8 2 7 P: 2 2 2 4 Quick fix H

1st.(NH4)2Cr2O7 N2 + Cr2O3 + 4H2O

N H Cr O R: 2 8 2 7 P: 2 8 2 7

DONE!

#4] Zn3Sb2 + H2O Zn(OH)2 + SbH3

Zn Sb H OR: 3 2 2 1P: 1 1 5 2You can start with Zn or Sb or both simultaneously.

Zn3Sb2 + H2O 3Zn(OH)2 + 2SbH3

Zn Sb H OR: 3 2 2 1P: 3 2 12 6

Zn3Sb2 + H2O 3Zn(OH)2 + 2SbH3

• Notice that the ratio of H:O is still 2:1 in the new products. Adjust H2O’s coefficient and you’re done.

• Zn3Sb2 + 6 H2O 3 Zn(OH)2 + 2 SbH3

• See? This really isn’t so hard after all. Take your time & switch between products’ and reactants’ total # of elements.