Chapter 4.1

Chemical Reactions

Chemical Reactions

Chemical Change – the transformation of one or more substances into different substances with different properties

Demonstrations Lycopodium + oxygen in the

presence of heat Iron (III) chloride (0.2M)+ Sodium

hydroxide (1M) Lead (II) nitrate + potassium iodide Magnesium metal + hydrochloric

acid (1M) also try hydrogen gas test Urea + water

Clues to a chemical change Change in colour Energy is released or absorbed Gas is produced A precipitate (solid) forms from two liquids Difficult to reverse

NOTE: a change in state or dissolving a substance is NOT a chemical change

How can we speed up a reaction?

http://www.youtube.com/watch?v=OttRV5ykP7A&sns=em

In order for a reaction to occur, reactants must collide in the correct orientation and with the correct amount of energy

Methods of increasing speed

1. Decrease the volume of the reaction vessel

2. Increasing concentration3. Increase temperature4. Increase surface area 5. Add a catalyst (this decreases

the amount of energy needed for a reaction to occur but doesn’t get consumed in the reaction)

increases the number of collisions

Chemical Equations

Represent chemical reactions by using words or symbols and formulas

Starting materials are called “reactants”

New substances are called “products” An arrrow () is read as “produces” States of matter appear in brackets

(s)=solid (l)=liquid (g)=gas (aq) dissolved in water

Word Equations

Use words to represent reactions Use all of your naming rules to do this!Ex.Magnesium + Hydrochloric acid Magnesium chloride + Hydrogen gas

Copper (II) sulfate + Ammonium chloride Copper (II) chloride + Ammonium sulfate

Sodium metal + oxygen gas sodium oxide

Skeleton Equation An unbalanced equation that shows

all reactants and products in a chemical reaction written as formulas

Rules:-write the symbol of a metal element

that is NOT in a compound ex. “Iron Nail” is Fe

Skeleton Equations

-If the non-metal is part of Hockey stick and puck, write it as a diatomic molecule

H2, N2, O2, F2, Cl2, Br2, I2Ex. Oxygen gas reacts with fluorine gas O2 + F2

- Write the formula of any other compound using the rules you have learned

Law of Conservation of Mass

States that in a chemical reaction, the mass of the products ALWAYS EQUALS the mass of the reactants since elements cannot be created or destroyed in a chemical reaction, they can only be rearranged!

Formula Equations Notice states of matter are always

included Coefficients are used to show the

ratios of the different substances present in the reaction (follows the law of conservation of mass)

Ex.Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)

Balancing

Balance polyatomic ions first if the same ion appears on both sides of the equation

Balance all other elements except H and O

Balance H Balance O

ExamplesBalance the following chemical equations. 1. Fe + H2S04 Fe2(SO4)3 + H2

2. C2H6 + O2 H2O + CO2

3. KOH + H3PO4 K3PO4 + H2O

4. SnO2 + H2 Sn + H2O

Homework

p. 155 #3,5

worksheet