1

Chapter 11

Chemical Reactions

2 Section 11.1

Describing Chemical Reactions Objective 1: You will learn to identify when a chemical reaction takes place.

Objective 2: You will know what the “Law of Conservation of Mass” means.

Objective 3: You will be able to write both

word

and

formula

equations.

Objective 4: You will know what all the different symbols used in writing chemical equations mean.

How Do You Know A Rxn Has Occurred???

• Heat and/or light is produced light and heat rxn • Production of gas • Formation of a precipitate • Color change precipitate and color change 3

Law of Conservation of Mass Atoms are neither created or destroyed Antoine Lavoisier (1743-1794) 4

Communicating a chemical reaction

In a

sentence

every item is a word … Copper reacts with chlorine to form copper (II) chloride.

In a

word equation

copper + chlorine  some symbols used … copper (II) chloride In a

formula

all symbols used … Cu(s) + Cl 2 (g)  CuCl 2 (s) 5

 All chemical reactions… have two parts:

1. Reactants

start with = the substances you  

2. Products

= the substances you end up with The reactants will turn into the products.

Reactants  Products 6

Symbols in equations? – Text page 323  the arrow separates the reactants from the products (arrow points

to

products)  –Read as: “reacts to form” or yields The plus sign means “and”    (s) after the formula = solid: Fe

(s)

(g) after the formula = gas: CO

2(g)

(l) after the formula = liquid: H

2

O

(l)

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Symbols used in equations  (aq) after the formula = dissolved in water, an aqueous solution: NaCl

(aq)

is a salt water solution  used after a product indicates a  gas has been

produced

: H

2

 used after a product indicates a solid has been

produced

: PbI

2

 8

Symbols used in equations ■

double arrow indicates a reversible reaction (more later)

■   

, shows that heat is supplied to the reaction

■

is used to indicate a catalyst is supplied

(in this case, platinum is the catalyst) 9

What is a catalyst?

 A substance that speeds up a reaction, without being changed or used up by the reaction.

 Enzymes are biological or protein catalysts in your body.

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1.

Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.

2.

Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

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Now, read these equations:

Fe (s) + O 2(g)



Fe 2 O 3(s) Cu (s) + AgNO 3(aq)



Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g) N 2(g) + O 2(g)

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Homework 11.1 and 11.2

Page 347

36, 39, 40, 42, 43, 44, 45a, 46, 47a, 48a, 49a, 50, 51a, 52 a-e 13