chapter 11: chemical reactions - wordpress.com · chemical reactions what is a chemical reaction?...
TRANSCRIPT
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CHAPTER 11: CHEMICAL
REACTIONS Mrs. Brayfield
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WRITING EQUATIONS
Write the chemical equation for the following:
Magnesium metal reacts with hydrochloric acid to
form aqueous magnesium chloride and hydrogen gas
Mg s + HCl aq → MgCl2 aq + H2(g)
Sulfur burns in oxygen to form sulfur dioxide
S s + O2(g) → SO2(g)
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CHEMICAL REACTIONS
What is a chemical reaction?
It is where one or more things changes
What are examples of chemical reactions?
How can we describe what happens in chemical
reactions?
Reactants → Products
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CHEMICAL EQUATIONS
A chemical equation is a representation of a
chemical reaction
For example the reaction between iron and oxygen:
Fe + O2 → Fe2O3
A skeleton equation is a chemical equation that
does not indicate the relative amounts of the
reactants and products
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SYMBOLS IN CHEMICAL EQUATIONS
(on page 348)
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BALANCING CHEMICAL EQUATIONS
When we look at the skeletal equation for a bike:
We don’t see the relative amounts of each part.
This is called an unbalanced equation
F + 1W + H + 1P → FW2HP2
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BALANCING CHEMICAL REACTIONS
The balanced equation for a bike would be:
The balanced equation is where each side of the
equation has the same number of atoms of each
element
F + 2W + H + 2P → FW2HP2
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BALANCING CHEMICAL EQUATIONS
The small whole numbers in front of the formulas
to balance the equation are called the coefficients
F + 2W + H + 2P → FW2HP2
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BALANCING CHEMICAL REACTIONS
So there are three steps when balancing chemical
reactions:
1. Write the skeleton equation
2. Use coefficients to balance the equation
3. Make sure that there are the same number of
atoms of each element on both sides of the
equation
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BALANCING CHEMICAL REACTIONS
The following reactions are balanced:
C(s)
Carbon + O2(g)
Oxygen CO2(g)
Carbon dioxide
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TYPES OF REACTIONS
In Chemistry we can classify reactions into five
general types:
1. Combination Reaction
2. Decomposition Reaction
3. Single-Replacement Reaction
4. Double-Replacement Reaction
5. Combustion Reaction
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COMBINATION (OR SYNTHESIS) REACTION
A combination reaction is where two or more
substances react to form a single new substance
Chemical example:
2Mg s + O2(g) → 2MgO(s)
+
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DECOMPOSITION REACTION
A decomposition reaction is where a single
compound breaks down into two or more simpler
products (the opposite of combination reactions)
Chemical example:
2NaN3 s → 2Na s + 3N2(g)
+
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SINGLE–REPLACEMENT REACTION
A single–replacement reaction is where one
element replaces a second element in a compound
Chemical example:
Zn s + Cu(NO3)2 aq → Cu s + Zn(NO3)2 (aq)
+ +
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DOUBLE–REPLACEMENT REACTIONS
A double–replacement reaction involves an
exchange of positive ions between two compounds
Chemical example:
FeS s + 2HCl aq → FeCl2 s + H2S(g)
+ +
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COMBUSTION
A combustion reaction is where an element or
compound (fuel) reacts with oxygen to form
carbon dioxide and water
The fuel is typically a hydrocarbon (compound
containing carbon and hydrogen)
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COMPLETE AND NET IONIC EQUATIONS
Sometimes in chemical equations we are only
interested in the gases, liquids, and solids that
form
The way that we can do this is by looking at the
complete ionic equation and the net ionic
equation
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COMPLETE IONIC EQUATION
The complete ionic equation shows dissolved ionic
compounds as dissociated free ions
If given the chemical equation of:
AgNO3 aq + NaCl aq → AgCl s + NaNO3(aq)
The complete ionic equation would be:
𝐴𝑔+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞 + 𝑁𝑎+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞
→ 𝐴𝑔𝐶𝑙 𝑠 + 𝑁𝑎+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞
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COMPLETE IONIC EQUATION
Notice that the nitrate ion and the sodium ion
appear on both sides of the equation
We can simplifying the equation by eliminating
these ions because they do not participate in the
reaction
𝐴𝑔+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞 + 𝑁𝑎+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞
→ 𝐴𝑔𝐶𝑙 𝑠 + 𝑁𝑎+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞
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NET IONIC EQUATION
When we simplify the equation and have only the
species undergoing the reaction, we have the net
ionic equation:
𝐴𝑔+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞 → 𝐴𝑔𝐶𝑙 𝑠
The ions that we cancelled are the ones that are
not directly involved in the reaction. These ions
are called spectator ions
𝑁𝑂3− 𝑎𝑞 , 𝑖𝑁𝑎+ 𝑎𝑞
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NET IONIC EQUATIONS
So the net ionic equation shows us what is
actually happening in the chemical reaction
ONLY single–replacement and double–
replacement reactions can be written as net ionic
equations
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PREDICTING THE FORMATION OF A SOLID
During a chemical reaction if there a solid
formed, we call that solid the precipitate
This solid “precipitates” out of solution because it is
insoluble in water (cannot be dissolved)
How can we tell if we formed a solid?
We use some general rules for solubility…
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SOLUBILITY RULES
(on page 372)
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PREDICTING PRODUCTS
Using all of our knowledge about the 5 types of
reactions, we can predict the products of
reactions using these steps:
1. Determine what kind of reaction the reactants will
most likely form
2. Look at the solubility rules to determine if a solid
formed
3. Balance the chemical reaction
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PREDICTING PRODUCTS
So if we have the following reactants:
𝐾𝐼 𝑎𝑞 , 𝑖𝑃𝑏𝑁𝑂3 𝑎𝑞
What would be the products?
Well, this is a double replacement reaction so…
𝐾𝐼 𝑎𝑞 + 𝑃𝑏𝑁𝑂3 𝑎𝑞 → 𝑃𝑏𝐼 ? + 𝐾𝑁𝑂3(? )
Did we form any solids?
YES!
𝐾𝐼 𝑎𝑞 + 𝑃𝑏𝑁𝑂3 𝑎𝑞 → 𝑃𝑏𝐼 𝑠 + 𝐾𝑁𝑂3(𝑎𝑞)