Balancing Chemical reactions
Chemical Reactions Review
A chemical reaction is a process in which one or more substances are converted into new substances that have different physical and chemical properties. In a chemical reaction, those substances present before the reaction are called the reactants. Substances produced in a chemical reaction are called the products. A chemical reaction takes place when an atom can find a more stable way to be joined to other atoms.
Scientists represent chemical reactions in chemical equations. Chemical equations can be in words or in formulas.
Example:
Solid sodium bicarbonate reacts with aqueous hydrogen chloride to produce aqueous sodium chloride, liquid water and carbon dioxide gas.
A chemical reaction is a process in which one or more substances are converted into new substances that have different physical and chemical properties. In a chemical reaction, those substances present before the reaction are called the reactants. Substances produced in a chemical reaction are called the products. A chemical reaction takes place when an atom can find a more stable way to be joined to other atoms.
Scientists represent chemical reactions in chemical equations. Chemical equations can be in words or in formulas.
Example:
Solid sodium bicarbonate reacts with aqueous hydrogen chloride to produce aqueous sodium chloride, liquid water and carbon dioxide gas.
Same reaction: NaHCO3 (s) + HCl (aq) --> NaCl (aq) + H22O (l) + CO2 (g)
In writing equations, it is always important to know the state of the atom or molecule you are working with. To show this, we use the following abbreviations:
(l) - liquid
(g) - gaseous
(s) - solid
(aq) - aqueous
Aqueous means dissolved in water.
Balancing Equations
In all reactions, the Law of Conservation of Matter is adhered to. Therefore, we must have the same number of atoms of each type of element on both sides of the reaction. In other words, if a reaction has 5 atoms of oxygen in the reactants, then it also has 5 atoms of oxygen in the products. No atoms of oxygen can be lost or gained during a chemical reaction. We accomplish this by placing necessary coefficients in front of the atoms or molecules in order to balance the number of each atom or group on each side of the arrow.
Examples:
Balance the following reaction:
(l) - liquid
(g) - gaseous
(s) - solid
(aq) - aqueous
Aqueous means dissolved in water.
Balancing Equations
In all reactions, the Law of Conservation of Matter is adhered to. Therefore, we must have the same number of atoms of each type of element on both sides of the reaction. In other words, if a reaction has 5 atoms of oxygen in the reactants, then it also has 5 atoms of oxygen in the products. No atoms of oxygen can be lost or gained during a chemical reaction. We accomplish this by placing necessary coefficients in front of the atoms or molecules in order to balance the number of each atom or group on each side of the arrow.
Examples:
Balance the following reaction:
__ H2SO4 (aq) + __ Mn (s) --> __ Mn(SO4)3 (aq) + __ H2 (g)
Solution: As you can see, there are not the same number of SO4 groups on both sides of the arrow. Therefore, a coefficient of 3 needs to be placed in front of the H2SO4 to make the SO4 equal on both sides:
3 H2SO4 (aq) + __ Mn (s) --> __ Mn(SO4)3 (aq) + __ H2 (g)
But this messes up the H2 now, so to fix that we need to put a coefficient of 3 in front of the H2:
3 H2SO4 (aq) + __ Mn (s) --> __ Mn(SO4)3 (aq) + 3 H2 (g)
The left over blanks can be left blank, because a blank defaults to a 1. Now we have 6 H on both sides, 3 SO4 on both sides and 1 Mn on both sides.
Practice Problems - Balance:
a) __ Cu (s) + __ HCl (aq) --> __ CuCl2 (aq) + __ H2 (g)
b) __SrF2 (aq) + __ Cu3PO3 (aq) --> __ CuF (aq) + __ Sr3(PO3)2 (s)
Practice Problems - Write Formulas and Balance:
c) Solid calcium is mixed with aqueous nickel (III) sulfate and makes aqueous calcium sulfate and solid nickel.
d) Solid copper (II) oxide mixes with carbon dioxide gas (CO2) to make solid copper (II) carbonate.
Answers to Practice Problems:
a) __ Cu (s) + 2 HCl (aq) --> __ CuCl2 (aq) + __ H2 (g)
b) 3 SrF2 (aq) + 2 Cu3PO3 (aq) --> 6 CuF (aq) + __ Sr3(PO3)2 (s)
c) 3 Ca (s) + Ni2(SO4)3 (aq) --> 3 CaSO4 (aq) + 2 Ni (s)
d) CuO (s) + CO2 (g) --> CuCO3 (s)
a) __ Cu (s) + __ HCl (aq) --> __ CuCl2 (aq) + __ H2 (g)
b) __SrF2 (aq) + __ Cu3PO3 (aq) --> __ CuF (aq) + __ Sr3(PO3)2 (s)
Practice Problems - Write Formulas and Balance:
c) Solid calcium is mixed with aqueous nickel (III) sulfate and makes aqueous calcium sulfate and solid nickel.
d) Solid copper (II) oxide mixes with carbon dioxide gas (CO2) to make solid copper (II) carbonate.
Answers to Practice Problems:
a) __ Cu (s) + 2 HCl (aq) --> __ CuCl2 (aq) + __ H2 (g)
b) 3 SrF2 (aq) + 2 Cu3PO3 (aq) --> 6 CuF (aq) + __ Sr3(PO3)2 (s)
c) 3 Ca (s) + Ni2(SO4)3 (aq) --> 3 CaSO4 (aq) + 2 Ni (s)
d) CuO (s) + CO2 (g) --> CuCO3 (s)