How Fast Are Chemical Reactions?
HOW FAST ARE CHEMICAL REACTIONS? THEORY The study of reaction rates, how fast or how slow a reaction takes place, is known as chemical kinetics. The rate of chemical reactions varies greatly. Some reactions, such as the explosion of an atom bomb are uncontrollable. Reactions like the decay of radioactive carbon (14C) are so slow that it takes centuries to see any noticeable change. Between the two extremes are reactions that can be measured in the laboratory.
There are several factors that affect reaction rates. They are listed in the Table 4.
Table 4. Factors that affect reaction rates
You’ll be studying various aspects of kinetics of three reactions.
A. Reaction between lead nitrate (PbNO3) and potassium chromate (K2CrO4) solutions
B. Reaction between potassium permanganate (KMnO4) and oxalate ion (C2O42-)
C. Iodine clock reaction
A. REACTION BETWEEN LEAD NITRATE AND POTASSIUM CHROMATE SOLUTIONS
Lead nitrate reacts with potassium chromate to form yellow lead chromate precipitate and aqueous potassium nitrate. The formation of a yellow precipitate indicates the completion of the reaction. The reaction is extremely fast.
Pb(NO3)2 (aq) + K2CrO4 (aq) → PbCrO4 (s) + KNO3 (aq)
B. REACTION BETWEEN POTASSIUM PERMANGANATE AND OXALATE ION
The reaction between potassium permanganate solution is an example of a redox reaction (oxidation-reduction reaction). The reaction is slow and takes a few minutes to occur. However, in the presence of a catalyst such as manganese(II) sulfate, the reaction occurs rapidly.
2 MnO4- + 5 C2O42- + 16 H+ 2 Mn2+ + 10 CO2 + 8 H2O
C. IODINE CLOCK REACTION
The reaction between iodate ion, IO3- and sulfite ion, SO32- to form iodide ion, I- and sulfate ion, SO42- is known as the iodine clock reaction.
KIO3 + Na2SO3 KI + 3 Na2SO4
When the sulfite ions are used up, the reaction is over, and the excess iodate ion, IO3- immediately reacts with the iodide ion, I- to form iodine, I2.
There are several factors that affect reaction rates. They are listed in the Table 4.
Table 4. Factors that affect reaction rates
You’ll be studying various aspects of kinetics of three reactions.
A. Reaction between lead nitrate (PbNO3) and potassium chromate (K2CrO4) solutions
B. Reaction between potassium permanganate (KMnO4) and oxalate ion (C2O42-)
C. Iodine clock reaction
A. REACTION BETWEEN LEAD NITRATE AND POTASSIUM CHROMATE SOLUTIONS
Lead nitrate reacts with potassium chromate to form yellow lead chromate precipitate and aqueous potassium nitrate. The formation of a yellow precipitate indicates the completion of the reaction. The reaction is extremely fast.
Pb(NO3)2 (aq) + K2CrO4 (aq) → PbCrO4 (s) + KNO3 (aq)
B. REACTION BETWEEN POTASSIUM PERMANGANATE AND OXALATE ION
The reaction between potassium permanganate solution is an example of a redox reaction (oxidation-reduction reaction). The reaction is slow and takes a few minutes to occur. However, in the presence of a catalyst such as manganese(II) sulfate, the reaction occurs rapidly.
2 MnO4- + 5 C2O42- + 16 H+ 2 Mn2+ + 10 CO2 + 8 H2O
C. IODINE CLOCK REACTION
The reaction between iodate ion, IO3- and sulfite ion, SO32- to form iodide ion, I- and sulfate ion, SO42- is known as the iodine clock reaction.
KIO3 + Na2SO3 KI + 3 Na2SO4
When the sulfite ions are used up, the reaction is over, and the excess iodate ion, IO3- immediately reacts with the iodide ion, I- to form iodine, I2.