Chemical Reactions. Describing Chemical Change Chemical reactions take place around you everyday...
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Transcript of Chemical Reactions. Describing Chemical Change Chemical reactions take place around you everyday...
Chemical Reactions
Describing Chemical Change• Chemical reactions take place
around you everyday
• Chemical reactions are expressed on paper as chemical equations
Describing Chemical Change• Word Equations
• Written in the form of reactants products (words only; arrow means “yields” or “produces”)
• Example:Iron + oxygen iron (III) oxide
Chemical Equations• Word equations adequately
describe reactions, but they are inconvenient
• In chemical equations, the formulas of the reactants are on the left, the formulas of the products are on the right
Chemical Equations
• Fe + O2 Fe2O3
• Equations such as the one above, which only show the formulas of the reactants and products are called skeleton equations
Chemical Equations• You can indicate states of
substances in parentheses• (s) – solid• (g) – gas• (l) – liquid• (aq) - aqueous
Balancing Equations• Remember the Law of Conservation of
Matter?
• All chemical reactions must obey that law, which means what you begin with must be the same as what you end with (although maybe in a different form)
Balancing Equations• Let’s go back to our example:
Iron + oxygen iron (III) oxideFe + O2 Fe2O3
Are there the same amounts of iron and oxygen on the reactants side and the products side?
Balancing Equations• An equation that does not indicate
the quantity of reactants needed to make the products is unbalanced
Balancing Equations• To balance an equation, numbers
called coefficients are placed in front of the symbols (when there is no coefficient, it is assumed to be one)
Balancing Equations
• Fe + O2 Fe2O3
How many Fe? Left = ? Right = ? How many O? Left = ? Right = ?
What coeffcients will we add to balance this equation?
Balancing Equations• Once you have added coefficients,
you check to make sure there are equal numbers of each element on both sides of the equation.
• Why?
Practice• Try balancing these equations on
your own at your seat.
• Sodium + chlorine sodium chloride
• CH4 + O2 CO2 + H2O
Practice - Answers• Sodium + chlorine sodium
chloride• 2Na + Cl2 2NaCl
• CH4 + 2O2 CO2 + 2H2O
Types of Reactions• Combination/Synthesis
• Two or more reactants make ONE product
2K + Cl2 2KCl2S + 3O2 2SO3
Types of Reactions• Decomposition
• ONE reactant is broken down into two or more products
(most require energy)
CaCO3 CaO + CO2
Types of Reactions• Single-Replacement
• A single element replaces a second element in a compound
(whether a reaction will occur depends on the activity series of metals – pg 217)
Mg + Zn(NO3)2 Mg(NO3)2 + ZnMg + LiNO3 no reaction
Types of Reactions• Double-Replacement
• Involve an exchange of positive ions between two reacting solutions (usually in solution and form percipitate)
3CuCl2 + 2Na3PO4 Cu3(PO4)2 + 6NaCl
Types of Reactions• Combustion
• Element or compound (usually hydrocarbon) reacts with oxygen. Products for a hydrocarbon are CO2 and H2O
2Mg + O2 2MgOCH4 + 2O2 CO2 + 2H2O
Practice • Predict the products of the
following reactions and balance:Na + Cl2 Mg + CuSO4 NaI + Pb(NO3)2
Practice - Answers2Na + Cl2 2NaClMg + CuSO4 MgSO4 + Cu2NaI + Pb(NO3)2 2NaNO3 + PbI2