Title: Chemical Reactions and Equations Chapter 9
1Chemical Reactionsand EquationsChapter 9
2Write the chemical reaction
- Write the formula equation for the following
- Ammonia reacts with hydrochloric acid to form
ammonium chloride.
3Learning Objectives
- Be able to balance chemical equations by applying
the law of conservation of mass. - Be able to recognize direct combination
(synthesis), decomposition, single displacement,
double displacement, combustion and
neutralization reactions.
4Law of Conservation of Matter
- Conservation of Matter in all chemical and
physical changes, matter is neither created or
destroyed - The total mass in a chemical reaction remains
constant - Antoine Lavoisier
- Made accurate and precise measurements during
chemical reactions
5Chemical Reactions
- A chemical change is really a chemical reaction
- Has 2 parts
- Reactants the substances you start with
- Products the substances you end up with
- The reactants turn into the products
- 4 Fe 3 O2 ? 2 Fe2O3
- Reactants ? products
6In a chemical reaction
- Atoms are rearranged into new molecules
- Can be described several ways
- 1. In a sentence
- Copper reacts with chlorine to form copper (II)
chloride. - 2. In a word equation
- Copper chlorine copper (II) chloride
- 3. In chemical formulas
- Cu Cl2 ? CuCl2
7Symbols in equations-
- the arrow ? separates the reactants from the
products - (s) after the formula solid
- (g) after the formula gas
- (l) after the formula liquid
- (aq) after the formula - aqueous solution,
dissolved in water.
8Symbols used in equations
- Double arrow indicates a reversible
reaction - shows that
heat is supplied to the reaction - is used to indicate a catalyst
is supplied, in this case, platinum.
9What is a catalyst?
- A substance that speeds up a reaction, without
being changed or used up by the reaction. - Enzymes are biological or protein catalysts.
10Balanced Equation
- Atoms cant be created or destroyed
- All the atoms at the beginning must appear in the
end - A balanced equation has the same number of atoms
of each element on both sides of the equation
11O
C
C
O
O
O
- C O2 CO2
- This equation is already balanced
- What do we do when an equation is not balanced?
12O
C
C
O
O
- C O2 CO
- We need one more oxygen in the products.
- Cant change the formula, because it describes
what the substance is (carbon monoxide in this
example)
13C
O
O
C
O
C
O
- Must be used to make another CO
- But where did the other C come from?
14C
C
O
O
O
C
O
C
- Must have started with two C
- 2 C O2 2 CO
15Rules for balancing
- Assemble, write the correct formulae for all the
reactants and products - Count the number of atoms of each type appearing
on both sides - Balance the elements one at a time by adding
coefficients (the numbers in front) - save H and
O until last! - Check to make sure it is balanced.
16Never
- Never change a subscript to balance an equation.
- If you change the formula you are describing a
different reaction. - H2O is a different compound than H2O2
- Never put a coefficient in the middle of a
formula - 2 NaCl is okay, Na2Cl is not.
17Balancing Equations Examples
- H2 (g) O2 (g) ? H2O (l)
-
- Zn HCl ? H2 ZnCl2
-
- Pb (NO3)2 K2S ? PbS KNO3
-
18Try a couple
- Write the balanced chemical equation for
dinitrogen pentoxide reacts with water to produce
nitric acid.
N2O5 H2O ? HNO3
19Try a couple
- Write the balanced chemical equation for
magnesium reacts with titanium (IV) chloride to
produce magnesium chloride and titanium.
Mg TiCl4 ? MgCl2 Ti
20Balance the following
- iron(II) chloride sodium phosphate ? sodium
chloride iron (II) phosphate - FeCl2 Na3PO4 ? NaCl Fe3(PO4)2
21Balance the following- Combustion Reaction (CO2
and H2O are the products)
- Write a balanced chemical equation for the
reaction in which benzene (C6H6) reacts with
oxygen gas to produce carbon dioxide and water. - C6H6 O2 ? CO2 H2O
22Five General Types of Chemical Reactions
- Direct Combination (Synthesis)
- Decomposition
- Single-Replacement
- Double-Replacement
- Combustion
-
- By knowing the type of reaction that is
occurring, you can predict the products that will
be formed.
23I. Direct Combination Reactions (also called
synthesis reactions).
- General form A B ? AB
- (two reactants make a single product)
- A, B elements or compounds
- AB compound consisting of A and B
- This is the only type of chemical reaction in
which there is a single product formed. This
single product is always more complex than the
reactants.
24Examples of Synthesis Reactions
- calcium oxygen yields calcium oxide 2Ca O2
? 2CaO - carbon dioxide water yields carbonic acid
- CO2 H2O ? H2CO3
- Notice All equations show two (or more)
reactants, but only one product. - http//www.ric.edu/ptiskus/reactions/Index.htm
25II. Decomposition Reactions
- General form AB ? A B
- (one reactant makes two or more products)
- AB compound
- A, B elements or simpler compounds
- This is the only type of chemical reaction in
which there is a single reactant. This single
reactant is always more complex than the
products.
26Decomposition Reactions Examples
- water yields hydrogen and oxygen
- 2H2O ? 2H2 O2
- marble (calcium carbonate) yields calcium oxide
and carbon dioxide - CaCO3 ? CaO CO2
- Notice all equations show a single reactant
decomposing into two (or more) products. - http//www.ric.edu/ptiskus/reactions/Index.htm
27III. Single-Replacement Reactions
- General Form A BX ? AX B
- One element and one compound recombine (switch
partners) - AX, BX ionic compounds
- A, B elements
- X ion that switches partners
- This is the only type of chemical reaction where
a compound reacts with an element to make another
compound and element.
28Single-Replacement Examples
- magnesium metal and copper (II) sulfate
- Mg CuSO4 ? MgSO4 Cu
- iron metal and copper (II) sulfate)
- Fe CuSO4 ? FeSO4 Cu
- Notice In both reactions, an element combines
with a compound to create a new compound and a
different element - www.ric.edu/ptiskus/reactions/Index.htm
29IV. Double-Replacement Reactions
- General form AX BY ? AY BX
- (Positive ions in two compounds are exchanged)
- A,B positive ions
- X,Y negative ions
- This is the only type of chemical reaction with
two compounds as reactants and two compounds as
products.
30Double Replacement Examples
- calcium carbonate and hydrochloric acid yield
calcium chloride and carbonic acid - CaCO3 2HCl ? CaCl2 H2CO3
- Notice in this reaction, two ionic compounds
exchange ions to form two new ionic compounds - www.ric.edu/ptiskus/reactions/Index.htm
31Rules of Double-Displacement Reactions
- Reactants must be dissolved in water (releasing
the ions). - Will occur if one of the products
- is a molecule (covalent),
- a precipitate (solid comes out of solution), or
- an insoluble gas.
32V. Combustion Reactions
- General Form
- CxHy O2 ? H2O CO2
- (hydrocarbon and oxygen react to form carbon
dioxide and water) - This is the only type of chemical reaction where
something reacts with oxygen and forms carbon
dioxide and water
33Combustion Examples
- Methane reacts with oxygen
- CH4 (methane) 2O2 ? 2H2O CO2
- Gasohol reacts with oxygen
- C2H5OH (gasohol) 3O2 ? 3H2O 2CO2
- Notice in both cases, water and carbon dioxide
are the products. - www.ric.edu/ptiskus/reactions/Index.htm
34Convert these to equations
- Solid iron (III) sulfide reacts with gaseous
hydrogen chloride to form iron (III) chloride and
hydrogen sulfide gas. - Nitric acid dissolved in water reacts with solid
sodium carbonate to form liquid water and carbon
dioxide gas and sodium nitrate dissolved in
water.