Multiple choice: Show a. Which of the following is not a characteristic of a chemical change? i. It is irreversible. ii. No net energy change is involved. iii. A new substance is formed. iv. Involves absorption or liberation of energy. b. A reaction of a type: AB + CD → AD + CD, involves i. No chemical change ii. Decomposition of AB and CD iii. Exchange of ions of AB and CD iv. Combination of AB and CD c. The reaction BaCl2(aq) + H2SO4(aq) → BaSO4(s) + 2HCl(aq) is i. Displacement reaction ii. Neutralisation reaction iii. Decomposition reaction iv. Double displacement reaction d. Thermal decomposition of sodium carbonate will produce i. Carbon dioxide ii. Oxygen iii. Sodium hydroxide iv. No other product Chapter 4. Chemical Reactions and Equations
Three classifications of chemical reactions will be reviewed in this section. Predicting the products in some of them may be difficult, but the reactions are still easy to recognize. A (sometimes also called a combination reaction or a synthesis reaction) produces a single substance from multiple reactants. A single substance as a product is the key characteristic of the composition reaction. There may be a coefficient other than one for the substance, but if the reaction has only a single substance as a product, it can be called a composition reaction. In the reaction 2H2(g) + O2(g) → 2H2O(ℓ) water is produced from hydrogen and oxygen. Although there are two molecules of water being produced, there is only one substance—water—as a product. So this is a composition reaction. A starts from a single substance and produces more than one substance; that is, it decomposes. One substance as a reactant and more than one substance as the products is the key characteristic of a decomposition reaction. For example, if we look at the decomposition of sodium hydrogen carbonate (also known as sodium bicarbonate): 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(ℓ) We can see that sodium carbonate, carbon dioxide, and water are produced from the single substance sodium hydrogen carbonate. Composition and decomposition reactions are difficult to predict; however, they should be easy to recognize. ProblemsIdentify each equation as a composition reaction, a decomposition reaction, or neither.
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Test YourselfIdentify the equation as a composition reaction, a decomposition reaction, or neither. C3H8 → C3H4 + 2H2 AnswerDecomposition. A combustion reaction occurs when a reactant combines with oxygen, many times from the atmosphere, to produce oxides of all other elements as products; any nitrogen in the reactant is converted to elemental nitrogen, N2. Many reactants, called fuels, contain mostly carbon and hydrogen atoms, reacting with oxygen to produce CO2 and H2O. For example, the balanced chemical equation for the combustion of methane, CH4, is as follows: CH4 + 2O2 → CO2 + 2H2O Kerosene can be approximated with the formula C12H26, and its combustion equation is 2C12H26 + 37O2 → 24CO2 + 26H2O Sometimes fuels contain oxygen atoms, which must be counted when balancing the chemical equation. One common fuel is ethanol, C2H5OH, whose combustion equation is C2H5OH + 3O2 → 2CO2 + 3H2O If nitrogen is present in the original fuel, it is converted to N2, not to a nitrogen-oxygen compound. Thus, for the combustion of the fuel dinitroethylene, whose formula is C2H2N2O4, we have 2C2H2N2O4 + O2 → 4CO2 + 2H2O + 2N2 ProblemsComplete and balance each combustion equation.
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Test YourselfComplete and balance the combustion equation for cyclopropanol, C3H6O. AnswerC3H6O + 4O2 → 3CO2 + 3H2O Propane is a fuel used to provide heat for some homes. Propane is stored in large tanks like that shown here.
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Media AttributionsExample 4.10
Which is a characteristic of a decomposition reaction?In a decomposition reaction, a single reactant is divided into two or more simpler substances. The unique characteristic of a decomposition reaction, which can be used to distinguish this pattern from the remaining classifications, is that only a single substance can be represented on the left side of a reaction arrow.
Which of the following is not a decomposition reaction?Solution: CH4 + 2O2 → CO2 + 2H2Ois not a decomposition reaction.
Which among the following is not the characteristic of reaction?The correct answer is b) no net energy is involved.
Which is a characteristic of a decomposition reaction quizlet?Which is a characteristic of a decomposition reaction? Substance P replaces X in the compound XY. Substance XYZ breaks down into X, Y, and Z.
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