18 Questions
What type of reaction takes place when reacting particles establish close contact?
Precipitation reaction
Give an example of a reaction that occurs explosively on close contact.
Iodine and phosphorus
What initiates reacting particles to move faster and collide more frequently?
Heating
How are most chemical reactions brought about?
By heating the reactants together
In which reaction do molecules of the reactant absorb light energy and react rapidly?
Photochemical reactions
How are many reactions brought about?
By passage of an electric current through the reactants
What type of reaction proceeds with the absorption of light energy?
Photochemical reaction
In what type of reaction do silver salts need to be kept in dark-colored bottles?
Photochemical reaction
What is the product of the reaction 2NH3 -> 4NO + N2 + H2O?
4NO + N2 + H2O
What is the product of the reaction CaCO3 -> CaO + CO2?
CaO + CO2
What type of reaction proceeds with the absorption of electrical energy?
Electrochemical reaction
What is the term used for a chemical change brought about by altering conditions or supplying energy?
Chemical changes
Explain how precipitation reactions are used to identify positive radicals in salts with different cations.
Precipitation reactions involve the formation of an insoluble solid when two solutions are mixed. By using specific reagents, different cations can be identified based on the precipitate formed.
Define double neutralization reaction and provide a suitable representation.
A double neutralization reaction involves the reaction between two acids and two bases to form two different salts and water. It can be represented as: acid1 + base2 = salt1 + water; acid2 + base1 = salt2 + water.
Explain energy changes in a chemical reaction and provide an example for each of the following: exothermic, endothermic reactions.
In a chemical reaction, energy changes occur due to the breaking and forming of bonds. An example of an exothermic reaction is the combustion of methane: CH4 + 2O2 -> CO2 + 2H2O + energy. An example of an endothermic reaction is the reaction of barium hydroxide octahydrate with ammonium thiocyanate: Ba(OH)2.8H2O + 2NH4SCN -> Ba(SCN)2 + 2NH3 + 10H2O.
Provide a balanced equation for a photochemical reaction.
An example of a photochemical reaction is the decomposition of hydrogen peroxide in the presence of light: 2H2O2 -> 2H2O + O2.
Give a balanced equation for an electrochemical reaction.
An example of an electrochemical reaction is the oxidation of zinc in an acidic solution: Zn + 2H+ -> Zn2+ + H2.
State the different forms of reactions initiated by the supply of energy and provide a suitable example for each form.
Reactions initiated by the supply of energy can include thermal decomposition (e.g., decomposition of hydrogen peroxide), electrolysis (e.g., electrolysis of water), and photolysis (e.g., photolysis of silver chloride).
Study Notes
Chemical Reactions
- When reacting particles establish close contact, a chemical reaction takes place.
- An example of a reaction that occurs explosively on close contact is the reaction between potassium and chlorine.
Factors Affecting Chemical Reactions
- Reacting particles move faster and collide more frequently when initiated by an increase in temperature, concentration, or the presence of a catalyst.
Types of Chemical Reactions
- Most chemical reactions are brought about by the supply of energy, such as heat, light, or electrical energy.
- Photochemical reactions occur when molecules of the reactant absorb light energy and react rapidly, such as the reaction between hydrogen and chlorine.
- Electrochemical reactions proceed with the absorption of electrical energy, such as the electrolysis of water.
- Silver salts need to be kept in dark-colored bottles to prevent photochemical reactions.
Reaction Products
- The product of the reaction 2NH3 → 4NO + N2 + H2O is nitrogen oxides and water.
- The product of the reaction CaCO3 → CaO + CO2 is calcium oxide and carbon dioxide.
Chemical Change
- A chemical change can be brought about by altering conditions or supplying energy, and this is termed as activation.
Precipitation Reactions
- Precipitation reactions are used to identify positive radicals in salts with different cations by precipitating the respective ions.
Double Neutralization Reaction
- A double neutralization reaction is a reaction in which two salts are formed by the reaction of two different acids and bases, represented as A + B → C + D.
Energy Changes in Chemical Reactions
- Exothermic reactions release energy, such as the combustion of methane, where heat is released.
- Endothermic reactions absorb energy, such as the decomposition of calcium carbonate, where heat is absorbed.
Balanced Equations
- A balanced equation for a photochemical reaction is 2H2 + Cl2 → 2HCl.
- A balanced equation for an electrochemical reaction is 2H2O → 2H2 + O2.
Forms of Reactions Initiated by Energy Supply
- The different forms of reactions initiated by the supply of energy include thermal, photochemical, and electrochemical reactions.
- Examples include:
- Thermal reaction: Decomposition of calcium carbonate
- Photochemical reaction: Reaction between hydrogen and chlorine
- Electrochemical reaction: Electrolysis of water
Test your knowledge on chemical reactions that involve the absorption of light energy and electrical energy. Identify examples of photochemical and electrochemical reactions.
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