Classifying equations tutorial:

Transcription

1 Classifying equations tutorial: Students are required to classify 5 kinds of equations. Indicator C-4.1 Indicator C-4.1 in the South Carolina Science Standards students should be able to analyze and balance equations for simple synthesis, decomposition, single replacement, double replacement, and combustion reactions. Prerequisite knowledge In Physical Science, students were supposed to have learned to: Apply a procedure to balance equations for a simple synthesis or decomposition reaction. (PS-4.9) Recognize simple equations (including single replacement and double replacement) as being balanced or not balanced. (PS-4.10) In this unit of chemistry students should: Classify typical equations based on the composition of the reactants Single replacement Double replacement Synthesis (composition) Decomposition Combustion Balance any reaction when given the reactants and the products, including the notations used to indicate the phase of the substance. Cl 2 (g) chlorine gas H 2 O(l) water as a liquid NaCl(s) sodium chloride as a solid NaCl(aq) sodium chloride dissolved in water Let s break each of these down separately: Classify typical equations based on the composition of the reactants Single replacement In a single replacement reaction you can think of the reactants (the s listed on the left side of the equation) as a and a. In a single replacement reaction the replaces one of the 2 parts of the. In a single replacement reaction metals replace metal ions, metals replace hydrogen cations (H + ), or halogens replace monoatomic halogen anions. You may recall that monoatomic halogen anions always have a 1 charge. Here are 2 illustration forms of single replacement reactions: Illustration reaction #1: A + BC AC + B Illustration reaction #2: A + BC BA + C The order of the s is not important. Reactant A can be written 1 st or BC can be written 1 st. Likewise the order of the products is not important. AC can be written 1 st or B can be written 1 st in the products of illustration reaction #1. Also, products BA can be written 1 st or C can be written 1 st in the products of illustration reaction #2.

2 Students need to be able to look at the reactants in a potential reaction and determine my visual inspection/analysis that the reaction has the potential to be a single replacement reaction. Illustration reaction #1: A + BC AC + B Example reaction #1: 3Mg(s) + CrBr 6 (aq) 3MgBr 2 (aq) + 6Cr(s) While the order of the s in the equation is not important (as long as you don t switch the products and reactants), the order in which you write the 2 parts of the compounds is. The more positive part is almost always written 1 st. When metals replace metals in single replacement reactions, the metals must always be written before the non-metal or the polyatomic anion. If a single replacement reaction is written in which a halogen replaces a halogen anion, then the halogen will go on the back because it will be the more negative part of the formula. Illustration reaction #1: A + BC BA + C Example reaction #2: Cl 2 (g) + NaBr(aq) NaCl(aq) + Br 2 (l) Note: There is nothing special about the order in which you list the reactants or products. In Illustration reaction #1 above, it is perfect acceptable for write BC before A, and it is just as acceptable to write C before BA. Note: I have balanced these equations for you in these examples, but you will have to learn to balance equations on your own. How you will be expected to do that will be shown to you later. Double replacement In a double replacement reaction you can think of the reactants (the s listed on the left side of the equation) as a and a. In a double replacement reaction the front and back parts of the first changes places with the 2 parts of the second. In a double replacement the reactants and products are almost always ionic compounds. Here are 2 illustration forms of single replacement reactions: Illustration reaction #2: AB + CD AD + CB Illustration reaction #2: AB + CD CB + AD As with the single replacement reactions, the order of the s in the equation is not important (as long as you don t switch the reactants and products) but the order of the parts of the compound are. The more positive part of the formula must be written first in the formula. This means that the front part in either reactant formula will remain the front part in the product formula. Illustration reaction #2: AB + CD AD + CB Example reaction #3: Ba(OH) 2 (aq) + MgCl 2 (aq) Mg(OH) 2 (s) + BaCl 2 (aq)

3 Note: Again, there is nothing special about the order in which you list the reactants or products. In Illustration reaction #1 above, it is perfect acceptable for write CD before AB, and it is just as acceptable to write CB before AD. Note: Again I have balanced this equation for you in this example, but you will have to learn to Synthesis (composition) You can think of a synthesis reaction as 2 or more reactants combining into a single or at the very least a smaller number of products. Here is an illustration form of a single replacement reaction: Illustration reaction #3: A + B AB As with the previous reactions, the order of the s in the reactants side of the equation (the left side) is not important but the order of the parts of the compound are. The more positive part or more electronegative part) of the formula must be written first in the formula. This means that the front part in either reactant formula will remain the front part in the product formula. Note: Again I have balanced this equation for you in this example, but you will have to learn to Decomposition You can think of a decomposition reaction as the opposite of synthesis; 2 or more reactants that combine into one product. Here is an illustration form of a single replacement reaction: Illustration reaction #4: AB A + B As with the previous reactions, the order of the s in the products side (right side) of the equation is not important (as long as you don t switch reactants and products) but the order of the parts of the compounds is. The more positive part or more electronegative part) of the formula must be written first in the formula. This means that the front part in either reactant formula will remain the front part in the product formula. Illustration reaction #3: A + B AB Example reaction #4: N 2 (g) + 3H 2 (g) 2NH 3 (g) Illustration reaction #4: AB A + B Example reaction #5: 2H 2 O 2 (l) O 2 (g) + 2H 2 O(l)

4 Note: Again I have balanced this equation for you in this example, but you will have to learn to Combustion Combustion is a complex set of reactions. Its broadest definition is any reaction between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. In this class, we will only deal with the simplest of combustion reactions; those between a hydrocarbon or organic fuel and oxygen from the air and which produce carbon dioxide gas, water (usually as a gas), light, and heat. Here is an illustration form of single replacement reaction: Hydrocarbon + O 2 (g) CO 2 (g) + H 2 O(g) + heat + light or organic fuel Contains carbon, hydrogen, and sometimes oxygen From the air or from the atmosphere Carbon dioxide water Usually this is a gas because of the heat Sometimes symbolized Δ Sometimes symbolized hν As with the earlier reactions, the order of the s in the equation is not important (as long as you don t switch the reactants and products) but the order of the parts of the compound are. Oxygen, carbon dioxide, and water have standard formulas. The hydrocarbon can be written in a condensed structural formula or a molecular formula (C x H y O z ). C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O(g) + heat + light Note: Again I have balanced this equation for you in this example, but you will have to learn to Classify the following reactions: Sample Problems 1) NaOH(aq) + KNO 3 (aq) NaNO 3 (aq) + KOH(aq) 2) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) 3) 2Fe(s) + 6NaBr(aq) 2FeBr 3 (aq) + 6Na(s) 4) CaSO 4 (s) + Mg(OH) 2 (s) Ca(OH) 2 (s) + MgSO 4 (aq) 5) NH 4 OH(aq) + HBr(aq) H 2 O(l) + NH 4 Br(aq) 6) Pb(s) + O 2 (g) PbO 2 (s) 7) Na 2 CO 3 (s) Na 2 O(s) + CO 2 (g)

5 1) double displacement 2) combustion 3) single displacement 4) double displacement 5) acid-base 6) synthesis 7) decomposition Solutions to the Sample Problems

6 1. Classify the Following s Chemical form 2H 2 (g) + O 2 (g) 2H 2 O(l) A + B AB Synthesis 2. Chemical form N 2 (g) + 3H 2 (g) 2 NH 3 (g) 3. Chemical form S 8 (s) + 12O 2 (g) 8SO 3 (s) 4. Chemical form 2N 2 (g) + O 2 (g) 2N 2 O(g) 5. Chemical form 2HgO(s) 2Hg(l) + O 2 (g) 6. Chemical form C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(g) 7. Chemical form Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) 8. Chemical form 2Na(s) + 2H 2 O(l) 2NaOH(aq) + H 2 (g) 9. Chemical form 2H 3 PO 4 (aq) H 4 P 2 O 7 (aq) + H 2 O(l)

7 10. Classify the Following s Chemical form C 10 H 16 (l) + 8Cl 2 (g) 10C(s) + 16HCl(g) 11. Chemical form 2Al(OH) 3 (s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + 6H 2 O(l) 12. Chemical form Fe(s) + O 2 (g) Fe 2 O 3 (s) 13. Chemical form Fe 2 (SO 4 ) 3 (aq) + 6KOH(aq) 3K 2 SO 4 (aq) + 2Fe(OH) 3 (s) 14. Chemical form 2C 7 H 6 O 2 (l) + 15O 2 (g) 14CO 2 (g) + H 2 O(l) 15. Chemical form 2Al(s) + Fe 2 O 3 (s) Al 2 O 3 (s) + 2Fe(s) 16. Chemical form Na 2 CO 3 (aq) + 2HCl(aq) 2NaCl(aq) + H 2 CO 3 (aq) 17. Chemical form 2K(s) + Br 2 (l) 2KBr(s) 18. Chemical form K 2 O(s) + H 2 O(l) 2KOH(aq)