The chemical equations for synthesis reactions fit the general pattern:

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Hollie Hensley
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1 Synthesis Reactions In a, two reactants combine to form one larger or more complex product. For this to occur, the reactants must first ; existing bonds between their atoms, and new bonds. The chemical equations for synthesis reactions fit the general pattern: Sample Problem 1: Writing Chemical Equations for Synthesis Reactions Write the balanced chemical equation for the reaction of magnesium with oxygen. SYNTHESIS REACTIONS INVOLVING HYDROGEN Hydrogen is unusual for a Group 1 element. Most Group 1 elements form ionic compounds when they bond with other elements. Hydrogen, however, usually forms molecular compounds. Ex:

2 The reaction of hydrogen with oxygen releases a great deal of, as well as water. This reaction has the potential to be an important source of green energy. However, since hydrogen does not occur naturally as an element, it has to be extracted from compounds that contain hydrogen. This, of course, requires energy. Therefore, hydrogen fuel can truly be considered "green" only if it is generated from environmentally friendly raw materials using a renewable energy source. Water would be a suitable raw material. Solar power would be a suitable energy source. SYNTHESIS REACTIONS NOT INVOLVING HYDROGEN The products of synthesis reactions of non-metals other than hydrogen are difficult to predict. The products of these reactions often depend on the reaction conditions. For example, two products are possible for the reaction of carbon with oxygen, depending on the availability of oxygen: In these cases, the only way to identify the reaction products is by conducting chemical tests. Synthesis Reactions Involving Compounds Compounds also can participate in synthesis reactions. For example, when carbon dioxide is bubbled into water the two compounds react to form a new substance. The new substance is an acid called carbonic acid.

3 Sulfur trioxide is another compound that is affecting the environment because of a synthesis reaction. It is produced during the combustion of fossil fuels. Water in the environment reacts with sulfur trioxide in a synthesis reaction to form sulfuric acid: Decomposition Reactions A chemical reaction in which one large compound breaks down or decomposes into two or more smaller substances is called a. The general pattern for a decomposition reaction is Simple ionic compounds such as potassium chloride, KCl, can be made to decompose into their elements. For example, potassium metal and chlorine gas are made industrially by passing electricity through molten potassium chloride:

4 Worksheet 2.2: Synthesis and Decomposition Reactions 1. Classify these reactions as synthesis or decomposition. Justify your choice. (a) 2 AI + 3 Br 2 2 AIBr 3 (b) 2 HCI H 2 + CI 2 (c) CaO + H 2 O Ca(OH) (d) P O 2 2 P 2 O 5 2. Predict the products of these synthesis or decomposition reactions. Write a balanced chemical equation to represent each reaction. (a) Z + S (d) K 2 O (b) CaCI 2 (e) AICI 3 (c) NH 3 + HCI (f) Mg(OH) H 2 O + 3. Hydrogen peroxide forms gas bubbles when it is added to blood. The other reaction product is water. Inserting a glowing splint into a sample of this gas causes the splint to relight. (a) Identify the gas. (b) Classify the reaction. (c) Write a balanced chemical equation for this reaction. 4. Write a balanced chemical equation for each of these reactions: (a) Aluminum metal readily reacts in air to form a hard protective coating of aluminum oxide. (b) Copper(lI) oxide and carbon dioxide are produced when copper(li) carbonate is heated. (c) Solid nitrogen triiodide is a shock-sensitive explosive that is stable when wet and explosive when dry. This compound decomposes rapidly to produce a gas when detonated. 5. Photosynthesis is a chemical process that occurs in green plants in which solar energy is converted into stored chemical energy. This process is the basis of life on Earth. The overall chemical equation for photosynthesis is 6 CO 2(g) + 6 H 2 O (I) C 6 H 12 O 6(s) + 6O 2(g) Compare photosynthesis to the synthesis reactions discussed in this section. 6. Most fossil fuels contain traces of sulfur. When the fuel is burned, the sulfur impurities become a major cause of acid precipitation. Three chemical reactions are involved. Write a balanced chemical equation for each reaction. (a) Solid sulfur reacts with oxygen to form gaseous sulfur dioxide. (b) The product from (a) then further reacts with oxygen to form gaseous sulfur trioxide. (c) The product from (b) then reacts with droplets of water in the atmosphere to form sulfuric acid.

5 7. Sodium hydrogen carbonate (baking soda) easily decomposes to release sodium carbonate, water, and a gas. Cake batter rises because of the decomposition of sodium hydrogen carbonate. (a) What gas is produced? [Hint: It turns limewater cloudy.] (b) Write a balanced chemical equation for this reaction. 8. A red solid compound is heated in a test tube. The reaction produces a colourless gas that relights a glowing splint. After the test tube cools, a silver-coloured liquid metal element remains. (a) What type of chemical reaction occurred in the test tube? Why? (b) Identify the gaseous product. (c) Identify the metal. (d) Name and write the chemical formula for the red solid compound. (Use the higher ionic charge of the metal). (e) Write a balanced chemical equation for this reaction. 9. The decomposition of solid sodium azide, NaN3, is the chemical reaction that inflates automobile airbags during a collision. (a) Write a chemical equation for this reaction. Assume that the first products formed are both gases because of the high temperature of the reaction. (b) Research the risks and benefits associated with air bags. 10. Cement kiln operators sometimes supplement the fuel used in cement kilns with old car tires. Research the potential environmental benefits and threats of this practice. Communicate your findings in a Pros and Cons chart. In your opinion, should the practice be continued or banned?

Elements and Their Oxides

Elements and Their Oxides An oxide is a. Oxides can form when an element reacts with oxygen, often in air. This reaction can be rapid with the release of a great deal of energy, as in the combustion of