Balancing chemical Reactions tutorial By: Koolnish123 & CtRunner17

Does The Law of Conservation of Mass Apply? Yes! The law of conservation of mass was established in 1789 by French Chemist Antoine Lavoisier. The law states that matter cannot be destroyed or created in any ordinary chemical reaction. This simply means that the mass of the reactants must be equal to the mass of the product. This is the reason why we have to balance chemical reactions, so that there are the same amount of each element in the reactants as there are in the product. If the law of conservation of mass did not apply the equation H2 + O2 -> H2O would work. Since there are 2 hydrogen atoms and only 1 oxygen atom in the product, this breaks the law of conservation of mass. To make it correct the equation would have to be 2H2 + O2 -> 2H2O. Example on next slide. http://www.mi.mun.ca/users/edurnfor/1100/atomic%20structure/tsld004.htm

Unbalanced: H2 + O2 H2O 2 2 = 2 1 Balanced: 2H2 + O2 2H2O 4 2 = 4 2

Balancing Chemical Reactions: A chemical equation defines what happens in a chemical reaction. The reactants, or the two substances that you start with, are on the left, and the product, the substance on the right, is what you end up with. We already know about the law of conservation of mass, that matter cannot be created or destroyed in a chemical reaction. So our chemical equation must match that law. This means that the number atoms of each element in the reactant must be equal to the number of atoms of each element in the product. http://richardbowles.tripod.com/chemistry/balance.htm http://i60.photobucket.com/albums/h15/mvs1979/owlOMG.jpg

http://www-evasion. imag. fr/~Francois http://www-evasion.imag.fr/~Francois.Faure/doc/inventorMentor/sgi_html/figures/14.15.ex.14.3.gif If there are more or less atoms on the reactant side, we know that we must change the equation, because that matter hasn’t simply disappeared, but has become part of the product. You might think that you can just change the subscript, or the small number after the element abbreviation of the elements on each side to get it to match, but you can’t do that. If you change the subscript, you are actually changing the entire reaction. The subscripts of all reactants and products must remain exactly the same when balancing chemical equations. You must instead change the coefficient, or the number in front of each element or compound, to make the equation balanced. http://richardbowles.tripod.com/chemistry/balance.htm

When balancing equations, make sure that if you have a compound and element in the reactants, balance the elements last. Doing this will cut out unnecessary steps that might will occur later in the equations. For example, in the reaction carbon dioxide reacts with hydrogen to form methane gas and water vapor, we balance the carbon and oxygen elements first. http://richardbowles.tripod.com/chemistry/balance.htm CO2 + H2 CH4 + H2O 1 2 2 1 6 1

Remembering to balance the elements last, we have to balance the carbons and oxygen atoms first. We see that the carbons are already balanced, so we can move onto the oxygen. The product needs one more oxygen atom, so it becomes 2H2O, and the oxygen is balance. Now we have 2 hydrogen atoms on the right, but 8 on the left. To fix, this we multiply H2 by 4 to get 4H2 which equals 8 hydrogen atoms. The balanced equation is then. CO2 + 4H2 CH4 + 2H2O 1 2 8 1 8 2 If you try to balance the hydrogen first in this equation, you will end up doing extra steps at the end. By balancing the elements last, you will reduce the amount of you work you will have to do, and the amount the writing. http://richardbowles.tripod.com/chemistry/balance.htm

Bibliography Information: Pictures: “Law of Conservation of Mass” http://www.mi.mun.ca/users/edurnfor/1100/atomic%20structure/tsld004.htm “Balancing Chemical Reactions” http://richardbowles.tripod.com/chemistry/balance.htm Pictures: “Unbalanced Scale” http://www-evasion.imag.fr/~Francois.Faure/doc/inventorMentor/sgi_html/figures/14.15.ex.14.3.gif “Omg Owl” http://i60.photobucket.com/albums/h15/mvs1979/owlOMG.jpg