Chemical Reactions Writing and Balancing Chemical Equations Balancing

Chemical Reactions Writing and Balancing Chemical Equations

Balancing Chemical Equations �Chemical reactions result in chemical changes. �Chemical changes occur when new substances are created. �The original substance(s), called reactants, change into new substance(s) called products.

� Chemical reactions can be written in different ways. � A word equation: Ø Nitrogen monoxide + oxygen nitrogen dioxide • A symbolic equation: State of matter Ø 2 NO(g) + O 2(g) 2 NO 2(g) - Letters indicate the state of each compound Coefficients - indicate the ratio of compounds in the reaction - here, there is twice as much NO and NO 2 than there is O 2 (aq) = aqueous/dissolved in water (s) = solid ( l) = liquid (g) = gas

�Chemical change means new compounds are created. �BUT no new matter is created or destroyed; atoms are just rearranged. �All of the matter in the reactants = all of the matter in the products �John Dalton, 200 years ago, realized that atoms simply rearrange themselves during chemical reactions. �Number of each atom in reactants = number of each atom in products

�The Law of Conservation of Mass �In chemical reactions, atoms are neither created nor destroyed �Developed by Antoine Lavoisier and his wife Marie-Anne in the 1700 s �Mass of reactants = Mass of products

�The simplest form of chemical equation is a word equation ◦ Not much information other than the elements/compounds involved �Potassium metal + oxygen gas potassium oxide

�A skeleton equation shows the formulas of the elements/compounds ◦ Shows atoms, but not quantities of atoms �K(s) + O 2 (g) K 2 O(s)

�A balanced chemical equation shows all atoms and their quantities ◦ Balancing ensures that the number of each atom is the same on both sides of the reaction arrow ◦ Always use the smallest whole number ratio � 4 K(s) + O 2 (g) 2 K 2 O(s)

◦ To balance, attempt to find values that equate atoms on both sides ◦ Balanced equation: CH 4(g) + 2 O 2 (g) 2 H 2 O(l) + CO 2(g) 1 Carbon, 4 Hydrogen, (2 x 2) Oxygen 1 Carbon, (2 x 2) Hydrogen, (2 x 1)+2 Oxygen

� Balance the following � 1. ___S 8 + ___O 2 � 2. equations: ___SO 3 ___KCl + ___O 2 ___KCl. O 3 ___CH 4 + ___Al(OH)3 ____H 2 O � 3. � 4. ___C 3 H 8 + ___O 2 ___CO 2 + ___H 2 O ___NH 3 + ___Mg(OH)2 ___H 2 O � 5. ___Al 4 C 3 + ___Mg 3 N 2 +

1. __S 8 + _12_O 2 _8_SO 3 2. _2_KCl + _3_O 2 _2_KCl. O 3 3. _3_CH 4 + _4_Al(OH)3 ___Al 4 C 3 + _12_H 2 O 4. ___C 3 H 8 + _5_O 2 _3_CO 2 + _4_H 2 O 5. _2_NH 3 + _3_Mg(OH)2 ___Mg 3 N 2 + _6_H 2 O

�Balance chemical equations by following these steps: ◦ Trial and error will work, but can be very inefficient ◦ Balance compounds first, elements last ◦ Balance one compound at a time ◦ Only add coefficients; NEVER change subscripts! ◦ If H and O appear in more than one place, attempt to balance them LAST ◦ Polyatomic ions (such as SO 42–) can often be balanced as a whole group ◦ Always double-check after you think you are finished!