Transcript CHEMICAL REACTIONS

Section 4.1
CHEMICAL REACTIONS
• A chemical reaction occurs when 2 or
more substances combine to form a new
substance.
• Reactants – materials that are combined to
start a reaction
• Products – new materials produced by the
reaction
• A chemical reaction can be written as a word
equation, with reactants on the left and
products on the right.
• Label the reactants and products in the following
word equation:
wood + oxygen ---- carbon dioxide + water + energy
• A chemical reaction can be written as a word
equation, with reactants on the left and
products on the right.
• Label the reactants and products in the following
word equation:
REACTANTS
Left side
PRODUCTS
Right side
wood + oxygen ---- carbon dioxide + water + energy
Remember:
Indicators of Chemical Reactions are:
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•
color change
change in odor
formation of a solid (precipitate)
formation of a gas (bubbling)
release or absorption of energy
(turning hot or cold)
Chemical Reactions Involving Energy
• Exothermic reactions release energy to the
surroundings. (heat ‘exits’)
• Give 1 example:
• Endothermic reactions absorb energy from
their surroundings. (heat ‘enters’)
• Give 1 example:
Chemical Reactions Involving Oxygen
• A combustion reaction occurs when oxygen
reacts with a chemical to produce a new
substance and a release of energy. (burning)
• Corrosion occurs when oxygen in the air
reacts with a metal, such as the rusting of
iron.
• Cellular respiration takes place in body cells.
It is the reaction of oxygen with glucose from
food to produce water, carbon dioxide and
energy.
C6H12O6(s) + O2(g)  CO2(g) + H2O(l )+ 36 ATP (energy)
(glucose)
Write a word equation and then a chemical
equation for the following reactions:
1. When hydrogen peroxide (H2O2) is left
out in the sun it decomposes into water
and oxygen gas.
Write a word equation and then a chemical
equation for the following reactions:
1. When hydrogen peroxide (H2O2) is left
out in the sun it decomposes into water
and oxygen gas.
Hydrogen peroxide + sunlight
H2O2 + sunlight
water + oxygen
H2O + O2
2. Iron left exposed to the atmosphere rusts.
2. Iron left exposed to the atmosphere rusts.
iron + oxygen
iron oxide
Fe + O2
FeO
or
Fe + O2
Fe2O3
3. Sodium and bromine react explosively to
produce sodium bromide.
3. Sodium and bromine react explosively to
produce sodium bromide.
sodium + bromine
Na + Br2
sodium bromide + Energy
NaBr + Energy
• Do Reflection
page 162
# 4,5,8,9
Section 4.2 Conservation of Mass
• The Law of Conservation of Mass:
In any chemical reaction, the total mass of the
reactants is equal to the total mass of the products.
Matter is neither created nor destroyed during chemical
reactions, though it may change in appearance.
• Sometimes it may appear as though this law is not
upheld;
ex. when Alka-Seltzer is added to water,
fizzing occurs as the reaction proceeds
• We find the final mass of the products is less then
the initial mass of the reactants.
Why is this?
What is an open system?
• The law is proven in a closed system, where
additional materials are not able to enter or
leave during a chemical reaction.
• If the beaker were capped, the gas would be
forced to stay in the beaker.
• The final mass would then equal the initial
mass.
Reactants
Products
Section 4.3
Factors Affecting the Rate of Reaction
How to speed up chemical reactions (and get a date)
. Catalysts
• A catalyst helps a reaction proceed more quickly.
• It is not altered during the reaction, so it is NOT a
reactant.
• ex: In your intestine, many catalysts, called enzymes,
are working to speed the rate of breaking down food.
• Fun fact: without these enzymes each meal would take
100 years to digest!
Q: What does the enzyme catalase do? (see p.166)
• The enzyme helps the substrate it reacts with,
break down.
• Note that the enzyme is not changed by the
reaction.
2. Concentration
With more reactants, a reaction proceeds more
quickly. There are more atoms of each reactant
available to react.
3. Temperature
An increase in temperature also speeds the rate of
reaction.
This is because with more heat, atoms of each
reactant move faster and collide with each other
more often. Products then form more quickly.
4. Surface Area
When the surface area of a reactant is increased,
reaction rate speeds up. This occurs because
more of the reactant is available to react.
• Review for exam:
• P154 #10
• P 162 #8,9
• Questaplus and Exambank