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Balancing chemical equations 1. Complete the following sentences, using the words or groups of words in the box below. You may use some words more than once. • as small as possible |• decrease |• molecules |• quantities | |• balance |• different |• nature |• rearranging | |• bonds |• equal |• never |• release of a gas | |• characteristic properties |• heat |• new elements |• rules | |• check |• increase |• nuclear |• signs | |• chemical |• law of conservation |• nucleus |• state | |• chemical equation |of mass |• physical |• stoichiometry | |• coefficient |• mass of products |• precipitate |• subscript symbols | |• colour |• mass of reactants |• products |• transformed | |• counting |• molar mass |• proportions |• whole numbers | a)There are three types of changes in matter: ________________________ changes, chemical changes and ________________________ changes. b)A physical change occurs when the form or the ________________________ of a substance is changed. For example, when liquid water is cooled, it becomes ice.

Whether water is in liquid form or in the form of ice, the ________________________ that form water remain the same. The ________________________ of water do not change. c)A ________________________ change alters the ________________________ of a substance. The very nature of the ________________________ is altered: they are no longer the same after the change. This transformation involves ________________________ the bonds between the atoms and forming new molecules. d)A ________________________ transformation involves changes that occur in the ________________________ of the atom. The transformation causes the atoms to split and form ________________________. ) Chemical changes occur when the ________________________ between reactants (initial substances) are broken to form new ________________________ (final substances), whose characteristic properties are ________________________. During this process, the quantities of reactants ________________________, and the quantities of products ________________________. f) We can recognize that a chemical change has taken place by certain ________________________: the ________________________, the emission or absorption of ________________________, the emission of light, a change in ________________________, and the formation of a ________________________. ) A chemical change, or chemical reaction, can be represented by a ________________________, which shows how the change took place. It is useful to identify the ________________________ of the substances (solid, liquid, gas or aqueous solution) with ________________________ in parentheses to the right of the substance. h) The scientist Antoine Laurent de Lavoisier made this famous statement that explains the________________________: “Nothing is lost; nothing is created; everthing is ________________________. ” This means that the ________________________ before the chemical reaction is equal to the ________________________ after the reaction. ) To follow the law of conservation of mass, we must ________________________ chemical equations by ________________________ the number of atoms of each element on the reactants side and on the products side of the equation. The appropriate ________________________ must be placed in front of each substance so that the number of atoms on each side of the equation is ________________________. j) Certain ________________________ must be followed when balancing a chemical equation. The coefficients must be ________________________, and they must be ________________________. New substances must ________________________ be added, nor existing substances removed.

Subscripts in chemical formulas must ________________________ be changed. Finally, we must ________________________ the equation by comparing the number of atoms of each element on either side. k) When a chemical equation is properly balanced, we can find the ________________________ of reactants needed for a reaction and predict the resulting quantities of products. ________________________ is the study of these proportions. It is essential to maintain the ________________________ of the substances throughout the reaction. We can use ________________________ to convert moles into grams. 2. What kind of change is described by each of the following examples? |a) a worn tire | | | |b) limewater that turns white | | | |c) a bracelet that tarnishes | | | |d) the fission of a uranium nucleus | | | |e) rusting iron | | | |f) mercury that expands in hot weather | | | |g) the fusion of the nuclei of several atoms | | | |h) food being transformed into energy | | | |i) salt dissolving in water | | | |j) radium emitting radiation | | 3.

For each of the following examples, name at least one sign that a chemical change is occurring. a) A match burns. | | | b) A yellow substance appears when NaI is mixed with Pb(NO3)2. | | | c) Bubbles form when chalk is mixed with hydrochloric acid. | | | d) A bright light appears when a piece of magnesium is burned. | | 4. Write a chemical formula to represent the following situation. Aluminum oxide (AlO), commonly called alumina, is formed by the reaction between aluminum (Al) and oxygen (O2). Balance the equation. | | | | | | 5. Balance each of the following chemical equations by indicating the number of atoms in each molecule involved in the reaction. a) C(s)+ H2(g) + O2(g) ( CH3OH(g) | | | | | | | | | | | | | | | | | | | | | b)Al(s) + O2 (g) ( Al2O3(s) | | | | | | | | | | | | | | | | | | | | | c)C(s) + Cl2(g) + H2(g) ( CHCl3(g) | | | | | | | | | | | | | | | | | 6.

The decomposition of 10 g of copper oxide is represented by the following equation: 2 CuO(s) ( 2 Cu(s) + O2(g) If you obtain 8 g of copper, what amount of oxygen was released? Explain your answer. | | | | | | | | | | | | 7. Calculate the mass and the number of moles of silver produced if you make 10 mol of zinc react with sufficient silver nitrate. (The equation is not balanced. Zn(s) + AgNO3(aq) ( Ag(s) + Zn(NO3)2 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 8. What mass of glucose will be formed if you make 32 mol of hydrochloric acid react with sufficient carbon? (The equation is not balanced. ) HCl(l) + C(s) ( C10H16(aq) + Cl2(g) | | | | | | | | | | | | | | | | | | | | | | | | | 9. Given the reaction for the synthesis of ammonia: N2(g) + 3 H2(g) ( 2 NH3(g) How many moles of hydrogen are needed to produce 50 g of ammonia? | | | | | | | | | | | | | | | 10. Given the following equation: 2 Na(s) + 2 H2O(l) ( 2 NaOH(aq) + H2(g) How many moles of hydrogen will be produced by the complete reaction of 75 g of sodium? | | | | | | | | | | | | | | | | | ———————– Support activities – Second Year of Secondary Cycle Two |EST | | student BOOK: Chapter 4, pages 108–113 | | Related Handout: Concept review 15 | ACTIVITY 15 EST EST EST EST EST ———————– ©ERPI Reproduction and adaptation permitted solely for classroom use with Observatory. Observatory / Guide 11129-B