Revision exercises

Ex.1. Answer the following questions:

1. How do we call a process when one or more substances are converted into one or more different substances? 2. When did the concept of a chemical reaction appear? 3. What is synthesis? 4. How is the ratio of reactants and products in a chemical reaction called? 5. What reaction is said to be endothermic? 6. What conditions are necessary to begin a reaction? 7. What factors influence the reaction rate?

Ex.2. Match the words with their definitions:

1. precipitate	a. a large molecule consisting of chains or rings of linked monomer units, usually characterized by high melting and boiling points;
2. reduction	b. a chemical reaction in which the solute and solvent react to form a new compound;
3. elimination	c) an insoluble solid that emerges from a liquid solution;
4. fermentation	d. any chemical reaction that involves the gaining of electrons;
5. polymer	e. a polysaccharide that is composed of glucose monomers and is the main constituent of the cell wall of plants;
6. cellulose	f. any of a group of chemical reactions induced by microorganisms or enzymes that split complex organic compounds into relatively simple substances
7. solvolysis	g. a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism.

Ex.3. Say whether the following statements are true or false:

1. A chemical reaction rearranges the constituent atoms of the reactants to create different substances. 2. In reactions under normal conditions matter is neither created nor destroyed. 3. One mole of any element or compound contains different number of atoms or molecules. 4. Entropy is a measure of the number of ways in which energy can be distributed in any system. 5. Starch and cellulose are members of a class of compounds called hydrocarbons. 6. If the bond breaks with both electrons of the shared pair remaining with one fragment, this is called homolysis. 7. A detailed description of the changes in structure and bonding that take place in the course of a reaction, and the sequence of such events is called the reaction mechanism.

Ex.4. Insert the necessary word:

1. When making a new substance from other substances, chemists say that they carry out a ... . 2. In an ... reaction, energy as heat is evolved. 3. Chemical reactions commonly need an initial input of ... to begin the process. 4. Several factors influence ... rates, including the concentrations of reactants, the temperature, and the presence of catalysts. 5. The ... that separates is called a precipitate. 6. Simple ... reactions include the reactions of an element with oxygen. 7. ... reactions occur in a sequence of steps in which the product of each step is a reagent for the next. (energy, synthetic, chain, reaction, redox, exothermic, solid)