unit i: chemical reactions i.4 introduction to chemical equations
TRANSCRIPT
Unit I: CHEMICAL REACTIONS
I.4 Introduction to Chemical Equations
Chemical Change
One or more new substances are formed in a chemical reaction
New substances formed by a chemical reaction or chemical change have properties different from those of the starting materials
Chemical Reactions
In chemical reactions The starting
materials are called reactants
The resulting materials are called products
Signs --- that a chemical change has occurred
Bubbles of gas appear Precipitate forms
Formation of solids in liquids Change in colour
Clear cloudy New smells Reactant used up Difficult to reverse Smoke Energy (heat, light, sound) A change in volume A change in conductivity A change in melting or boiling point
Chemical Change
Chemical Reaction Equations
Is an equationequation that shows the chemicals used up and produced during a chemical reaction
REACTANTS REACTANTS PRODUCTS PRODUCTS
Chemical Word Equation
Uses words to describe the REACTANTS and PRODUCTS
Eg. Sodium and chlorine react to form sodium chloride
Coefficients
the numbers in front of symbols Refer to the numbers of molecules of
each species involved in reaction
Unit I: CHEMICAL REACTIONS
I.4 The Conservation Laws
System
Part of the universe being studied in a particular location
Closed System
A CLOSEDCLOSED system nothing can enter or leave the system
It exchanges energy (heat and work) but not matter with the environment.
Closed System
Open System
Open SystemOpen System Things can enter and leave the system It exchanges energy (heat and work)
and matter with the environment.
Open System
Open System
The Four Laws of Conservation
1. Law of Conservation of Mass The total mass in a closed system does
not change during a chemical reaction
The Four Laws of Conservation
2.2. Law of Conservation of AtomsLaw of Conservation of Atoms Total number and type of atoms in a
closed system does not change during a chemical reaction
MgMg
MgMg
MgMg
MgMgNaNa
Whoa! Where did you come
from!
The Four Laws of Conservation
3. Law of Conservation of Electrical Charge
The total electrical charge in a closed system does not change during a chemical reaction
The Four Laws of Conservation
4.4. Law of Conservation of EnergyLaw of Conservation of Energy The total energy in a closed system does
not change during a chemical reaction Relative types of energy may change but the
total amount of energy remains the same
The Four Laws of Conservation
The Four Laws of Conservation
Hebden
Do Exercises 1 and 2 on page 106 and 3 to 5 on page 107