Recognizing and Understanding Chemical Changes

What is a chemical change? Any change where a new substance is formed How do we know this has happened? 4 different things can happen: 1. change in colour 2. change in odour 3. formation of gas and/or solid 4. release or absorption of heat

Understanding Chemical Changes we need to first understand Kinetic Molecular Theory (KMT) to explain chemical changes Kinetic molecular theory (KMT): all matter is made up of particles continually moving in random motion Temperature (T) is used to measure speed of particles because if you increase T, speed of particles increases we use KMT and collision reaction theory to understand chemical changes

Collision Reaction Theory chemical reactions involve collisions the outcome of the collisions depends on the energy and orientation of the reactants an effective collision has the correct amount of energy and the proper orientation to allow the valence shells of the reactants to overlap this allows their electrons to rearrange and form bonds very few of the collisions between molecules are effective, but to..

To make a reaction faster: Increase the # of collisions (greater chance of a successful collision) Increase the # of effective collisions (more collisions with enough energy)

There are 4 variables we can change to make the reaction go faster 1. Temperature 2. Concentration 3. Surface Area 4. Catalysts

Temperature increase temperature, the speed of the molecules increases more molecules collide more often and more effectively

Concentration Increasing the concentration of the reactant increases the # of collisions between molecules

Surface Area Increasing the surface area of the reactants, increases the # of collisions that are effective between the molecules

Catalysts Catalyst: speeds up a chemical reaction, but is not consumed in the reaction reduce the collision energy required for the chemical reaction

Representing Chemical Reactions All chemical reactions can be represented in one of 2 ways: A word equation A chemical equation

1. Word Equations Word equation: a representation of a chemical reaction using only the names of the reactants and products Example:

2. Chemical Equations Chemical Equation: A representation of a chemical reaction that uses coefficients in front of the chemical formulas of reactants and products and states of matter of all compounds/elements. States of Matter: (s): solid (g): gas (l): liquid (aq): aqueous Example:

Balancing Equations Law of Conservation of Mass: States that in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products. Since the mass of the reactants is always equal to the mass of the products, we know that the # of each kind of atom is the same before and after the reaction. Procedure for Balancing a Chemical Equations 1. Balance all atoms other than oxygen and hydrogen 2. Balance hydrogen 3. Balance oxygen 4. Check to see if everything is balanced