Download chemical reaction?

Unit 7: Properties of Matter
Lesson 4: Chemical Reactions
Signs of a Chemical Reaction
• What is a chemical reaction?
Signs of a Chemical Reaction
• What is a chemical reaction?
– The process in which atoms are rearranged and
chemical bonds are broken and formed to
produce a chemical change of a substance
• What are the signs that a chemical reaction is
occuring?
Signs of a Chemical Reaction
• What is a chemical reaction?
– The process in which atoms are rearranged and
chemical bonds are broken and formed to produce a
chemical change of a substance
• What are the signs that a chemical reaction is
occuring?
–
–
–
–
Formation of a precipitate
Color change
Change in odor
Appearance of gas bubbles
Modeling Chemical Reactions
• What is a chemical formula?
Modeling Chemical Reactions
• What is a chemical formula?
– a combination of chemical symbols and numbers
to represent a substance
Modeling Chemical Reactions
• The chemical symbols in a formula tell what
types of elements make up a substance
• The ________________ in a chemical formula
tell how many of each type of atom are in a
molecule
Modeling Chemical Reactions
• The chemical symbols in a formula tell what types
of elements make up a substance
• The ________________ in a chemical formula tell
how many of each type of atom are in a molecule
• Example: The chemical formula for rust, or iron
oxide, is Fe2O3. How many iron atoms and how
many oxygen atoms are in one unit of iron oxide?
Modeling Chemical Reactions
• What are reactants and what are products in
terms of a chemical reaction?
Modeling Chemical Reactions
• What are reactants and what are products in
terms of a chemical reaction?
– Reactatnt: a substance that participates in a
chemical reaction
– Product: a substance that forms in a chemical
reaction
Modeling Chemical Reactions
• In the chemical formula
C + O2
CO2
What are the reactants and what is the
product?
Modeling Chemical Reactions
• In the chemical formula
C + O2
CO2
What are the reactants and what is the
product?
– Carbon and oxygen are the reactants, and carbon dioxide is
the product. One carbon atom and two oxygen atoms
combine to form one carbon dioxide molecule.
Balancing Equations
• Because of the law of conservation of mass,
chemical equations must show the same
numbers and kinds of atoms on both sides of
an arrow.
• To balance an equation, ________________
are placed in front of a chemical formula. Only
____________, not subscripts, can be
changed when balancing a chemical equation.
Balancing Equations
• Examples:
_____ Mg + ____ O2
_____ K + _____ O2
_____ H2O2
_____ MgO
_____ K2O
______ H2O + ______ O2
Energy can be Absorbed
• What is an endothermic reaction?
Energy can be Absorbed
• What is an endothermic reaction?
– A chemical reaction that requires the input of energy
– The energy taken in from the surroundings is
absorbed from the surroundings as ____________
– Therefore, endothermic reactions often feel
____________
– An example of an endothermic reaction is
__________________
Energy Can be Released
• What is an exothermic reaction?
Energy Can be Released
• What is an exothermic reaction?
– A chemical reaction in which energy is released to
the surroundings
– Exothermic reactions often feel __________
because energy is released as heat
– An example of an exothermic reaction is
_______________
Energy is Always Conserved
• What does the law of conservation of energy
state?
Energy is Always Conserved
• What does the law of conservation of energy
state?
– Energy cannot be created or destroyed. However,
energy can change form.
What affects the rates of reactions?
• Reactions can occur in less than a second or over
a matter of days.
• Reaction rates are affected by how often particles
_______________.
• The factors that affect reaction rates are
_________________ , ______________
_____________, _____________, and the
presence of a ________________.
Concentration
• Higher concentration = _____________
reaction rate
• Why?
Concentration
• Higher concentration = _____________
reaction rate
• Why?
– There are more reactants in a given volume,
therefore they are more likely to collide and react
Surface Area
• Higher surface area = ______________
reaction rate
• Why?
Surface Area
• Higher surface area = ______________
reaction rate
• Why?
– More reactant particles are exposed to one
another, so more collisions occur
Temperature
• Higher Temperature= _________________
reaction rate
• Why?
Temperature
• Higher Temperature= _________________
reaction rate
• Why?
– At higher temperatures, particles move more
quickly, and are more likely to collide and react
Catalyst
• A catalyst is a substance that changes the rate
of a chemical reaction without being used up
or changed very much.
• Catalysts usually ____________ reaction rate
by bringing together reactants
• _____________ are an example of a catalyst
found in living things