Chemistry Questions & Answers

6. During a chemical reaction, energy is either released or absorbed 7. Is the following sentence true or false? Physical and chemical changes can be either exothermic or endothermic changes. 8. What is an exothermic reaction? 9. Is the following sentence true or false? In exothermic reactions, the energy required to break the bonds in the reactants is greater than the energy released as the products form.

2. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the Circle the correct answer. products reactants Is the following sentence true or false? The formation of chemical bonds absorbs energy. Is the following sentence true or false? The heat and light given off by a propane stove result from the formation of new chemical bonds. The combustion of one molecule of propane \( \left(\mathrm{C}_{3} \mathrm{H}_{8}\right) \) results in the formation of \( 6 \mathrm{C}=\mathrm{O} \) double bonds and \( 8 \quad \mathrm{H} \) single bonds.

13. What is an oxidation-reduction reaction? 14. Calcium reacts with oxygen to form calcium oxide. Which reactant is oxidized in this reaction? 15. Is the following sentence true or false? When calcium reacts with oxygen, each calcium atom gains two electrons and becomes a calcium ion with a charge of \( 2- \). 16. Is the following sentence true or false? Oxygen must be present in order for an oxidation-reduction reaction to take place. 17. The process in which an element gains electrons during a chemical reaction is called

8. Lead(II) nitrate reacts with potassium iodide to form lead(II) iodide and potassium nitrate. Write the balanced equation for this double-replacement reaction. 9. Circle the letter of the correct answer. Calcium carbonate, \( \mathrm{CaCO}_{3} \) reacts with hydrochloric acid, HCl , in a double-replacement reaction. What are the products of this reaction? a. calcium chloride, \( \mathrm{CaCl}_{2} \), and carbonic acid, \( \mathrm{H}_{2} \mathrm{CO}_{3} \) b. calcium hydride, \( \mathrm{CaH}_{2} \), chlorine, \( \mathrm{Cl}_{2} \), and carbon dioxide, \( \mathrm{CO}_{2} \) c. calcium hydrogen carbonate, \( \mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2} \), and chlorine, \( \mathrm{Cl}_{2} \) d. calcium perchlorate, \( \mathrm{Ca}\left(\mathrm{ClO}_{4}\right)_{2} \), and methane, \( \mathrm{CH}_{4} \) 10. Is the following sentence true or false? A combustion reaction is a reaction in which a substance reacts with carbon dioxide, often producing heat and light. 11. Methane, \( \mathrm{CH}_{4} \), burns in oxygen to form carbon dioxide and water. Write the balanced equation for this reaction. 12. Is the following sentence true or false? The reaction that forms water can be classified as either a synthesis reaction or a combustion reaction.

2. Circle the letter of each equation that represents a synthesis reaction. a. \( 2 \mathrm{Na}+\mathrm{Cl}_{2} \longrightarrow 2 \mathrm{NaCl} \) b. \( 2 \mathrm{NaCl} \longrightarrow 2 \mathrm{Na}+\mathrm{Cl}_{2} \) c. \( 2 \mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{H}_{2}+\mathrm{O}_{2} \) d. \( 2 \mathrm{H}_{2}+\mathrm{O}_{2} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O} \) 3. Is the following sentence true or false? A decomposition reaction is the opposite of a synthesis reaction. 4. Write the equation for the decomposition of calcium carbonate into calcium oxid and carbon dioxide. 5. Circle the letter of the correct answer. Copper reacts with silver nitrate in a single-replacement reaction. What are the products of this reaction? a. copper(II) nitride and silver oxide b. copper(II) nitrate and silver c. copper(II) oxide and silver nitrate d. copper, nitrogen, and silver oxide

6. Is the following sentence true or false? A chemical equation must be balanced in order to show that mass is conserved during a reaction. 7. Circle the letter of the name given to the numbers that appear before the formulas in a chemical equation. \( \begin{array}{ll}\text { a. subscripts } & \text { b. mass numbers } \\ \text { c. atomic numbers } & \text { d. coefficients }\end{array} \) 8. Is the following sentence true or false? Because the equation \( \mathrm{N}_{2} \mathrm{H}_{4}+\mathrm{O}_{2} \longrightarrow \mathrm{~N}_{2}+\mathrm{H}_{2} \mathrm{O} \) has two nitrogen atoms on each side, the equation is balanced.

1. Is the following sentence true or false? The new substances formed as a result of a chemical reaction are called products. 2. Circle the letter of each sentence that is a correct interpretation of the chemical equation \( \mathrm{C}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2} \). a. Carbon and oxygen react and form carbon monoxide. b. Carbon and oxygen react and form carbon dioxide. c. Carbon dioxide yields carbon and oxygen. d. The reaction of carbon and oxygen yields carbon dioxide. 3. Is the following sentence true or false? The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.

Which of the following represents the sublevels from which the electrons are lost-when the atom of the element \( { }_{21} \mathrm{Sc} \) is converted to \( \mathbf{M}^{3+} \) ion ? \( \begin{array}{ll}\text { (i) } 3 s, 4 s & \\ \text { c) } 3 d, 4 p & \text { (d) } 4 s, 4 p\end{array} \)

2. Закончить уравнение химической реакции. Что является нуклеофилом в данной реакции? \( \mathrm{H}_{3} \mathrm{C}-\mathrm{O}-\mathrm{Na}+\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{I} \)

2. Закончить уравнение химической реа данной реакции? \( \mathrm{H}_{3} \mathrm{C}-\mathrm{O}^{-}-\mathrm{Na}+\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{I} \longrightarrow \)