What is a synthesis reaction? Lesson + KEY TERM synthesis reaction: combining of several substances to form a more complicated substance 85
LESSON 14 What is a synthesis reaction? Chemical reactions are happening around you all the time. A match burns. A car rusts. Food spoils. Leaves decay. These are just a few chemical reactions. Probably the most important chemical reactions take place in your body. They are happening this very moment. Digestion is a chemical process. So is respiration. In everyone of your trillions of cells, chemical reactions are taking place all the time. Life depends upon chemical reactions. There are several kinds of chemical reactions. One kind is the synthesis [SIN-thuh-sis] reaction. "Synthesis" means a putting together. A synthesis reaction combines substances, usually elements, to form a compound. When the compound forms, we say it has been synthesized. Below is a "model" of a synthesis reaction. A + B --~) AB Element + Element ~ Compound Let's study two synthesis reactions. RUSTING When iron rusts, it combines with oxygen. Remember this equation? 4Fe + 302 ~ 2Fe 2 0 3 Iron + Oxygen ~ Iron oxide (rust) link up E1ement + E1ement to form) Compound THE BURNING OF CARBON Charcoal is made of the element carbon (C). When carbon burns, it combines with oxygen. This produces the gas carbon dioxide (C0 2 ). C + 02 Carbon + Oxygen Element + Element link up ) to form Carbon dioxide Compound A synthesis reaction is like any other kind of chemical reaction. No matter is created. No matter is destroyed. The atoms just change their arrangement.
UNDERSTANDING SYNTHESIS REACTIONS Look at Figures A through E and read the explanation. Then answer the questions with each. When hydrogen explodes, it combines with oxygen. Water is produced. This equation shows what happens: 2H2 + 02 -----?> H 2 0 Hydrogen + Oxygen -----?> Water 1. Hydrogen is _ 2. Oxygen is _ 3. Water is _ a Figure A 4. Is the formation of water a synthesis reaction? 5. Why is the formation of water a synthesis reaction? _ b Figure B When powdered sulfur and iron filings are heated together, they form iron sulfide. This equation shows what happens: Fe + S -----?> FeS Iron + Sulfur -----?> Iron sulfide 1. Iron is _ 2. Sulfur is _ 3. Iron sulfide is _ 4. What happens to the iron and sulfur when they form iron sulfide? _ Figure C Figure D 87
Sodium combines with chlorine to form sodium chloride-common table salt. This equation shows what happens: ( I I 2Na + Cl 2 ---7 2NaCI Sodium + Chlorine ----7 Sodium chloride Figure E 1. Sodiumis _ 2. Chlorine is _ 3. Sodium chloride is _ 4. What kind of reaction is the formation of sodium chloride? _ Why? _ YOUR OWN WORDS 1. What does "synthesis" mean? _ 2. What does "synthesis reaction" mean? _ Two synthesis equations are shown below. They are different from the ones you have already seen. Equation I Equation II 3. How is Equation I different from the other synthesis equations in this lesson? 4. How is Equation II different from the other synthesis equations in this lesson? 88
IDENTIFYING SYNTHESIS REACTIONS Ten equations are listed below. Some are synthesis the correct box next to each equation. reactions. Some are not. Make a check (V') in 1. 2K + Br2 ~ 2KBr 2. 2~0 ~ 2~ + 02 3. 2NaCl~ 2Na + Cl 2 A Not a Equation Synthesis Synthesis Reaction Reaction 4. 4Au + 302 ~ 2Au20 3 5. 2Na + 2HCl ~ 2NaCl + H2 6. Cu + Br2 ~ CuBr 2 7. Zn+S~ZnS 8. 2Na + Br2 ~ 2NaBr 9. 2HgO ~ 2Hg + 02 10. 2Na + 12 ~ 2Nal TRUE OR FALSE In the space provided, write "true" if the sentence is true. Write 'false" if the sentence is false. 1. There is only one kind of chemical reaction. 2. A synthesis reaction separates a compound into its elements. 3. The reactants of every synthesis reaction are elements. 4. The product of a synthesis reaction is a compound. 5. Chemical reactions take place only in the laboratory. 89
WORD SEARCH The list on the left contains words that you have used in this Lesson. Find and circle each word where it appears in the box. The spellings may go in any direction: up, down, left, right, or diagonally. C T L A C I S Y H P A H 0 N L A C I M E H C MATTER POLYVALENT I Y I E L D S C N 0 D MASS M M C A L U M R 0 F M REACTANT T N A T C A E R T T Y FORMULA PHYSICAL N E L S H W V H G C L PRODUCT R I A L S S A Y L U L YIELDS CHEMICAL A L P B D H C Z L D I I S Y R A G L E Y 0 M J E R R R H D W I R P C L R E T T A M E P I REACHING OUT Most compounds made of only two elements have names ending in -ide. For example: Can you name these compounds? NaCl = sodium chloride K 2 S = potassium sulfide Formula Name 1. CaO 2. KI 3. NaBr 4. AgF - 5. MgCl 90