A chemical equation is a representation of a chemical process in the form of symbols for the substances involved in the reaction. It’s a way of depicting a chemical reaction with symbols and formulae for the components.
The chemical equation can be more informative in the following three ways.
- By characterizing the physical states of the reactants and products. Solids are represented by the letter’s,’ liquids by the letter ‘l,’ and gases by the letter ‘g.’ The symbol for aqueous solutions is (aq).
- By showing the temperature variations that occur during the process. For example, an exothermic process is one in which heat is released. A heat-absorbing reaction is known as an endothermic reaction.
- By describing the circumstances in which the reaction takes place. The catalyst’s symbol or formula is placed above or below the arrow sign if the reaction is taking place in the presence of a catalyst,
There are various conditions such as the heat, presence of a catalyst, the conditions of temperature, and pressure under which a reaction takes place. These conditions are discussed further below.
Chemical reaction in Presence of Heat
The heat of the reaction is the amount of heat that must be added or removed during a chemical reaction to keep all of the components present at the same temperature. The measured heat of reaction also represents the change in the thermodynamic quantity known as enthalpy, or heat content, which is the difference between the enthalpy of the substances present at the end of the reaction and the enthalpy of the substances present at the start of the reaction if the pressure in the vessel containing the reacting system is kept constant.
As a result, the heat of reaction measured under constant pressure is also known as the enthalpy of reaction, indicated by the symbol ΔH. The reaction is said to be endothermic if the heat produced by it is positive. The reaction is considered to be exothermic if the heat of the reaction is negative. If heat is required for a reaction to occur, the heat symbol delta (Δ) is placed over the equation’s arrow.
When nitrogen and oxygen are heated to an extremely high temperature, they combine to generate nitrogen monoxide, as shown in the reaction below.
N2 + O2 + Heat → 2NO
(Nitrogen) (Oxygen) (Nitrogen Monoxide)
Chemical reaction in Presence of a Catalyst
Any material that increases the rate of a process without being consumed is referred to as a catalyst. Enzymes, which are naturally occurring catalysts, catalyze several important metabolic reactions.
Metals and their oxides, sulphides, and halides, as well as the semimetallic elements boron, aluminium, and silicon, make up the majority of solid catalysts. Solid catalysts are usually dispersed in other substances known as catalyst supports; gaseous and liquid catalysts are commonly utilized in their pure form or combination with suitable carriers or solvents.
Catalytic action, in general, is a chemical reaction between a catalyst and a reactant that produces chemical intermediates that can react more readily with each other or with another reactant to produce the desired end product. The catalyst is regenerated during the reaction between the chemical intermediates and the reactants. The modes of reaction between the catalysts and the reactants vary greatly and are frequently complex in solid catalysts.
Acid-base reactions, oxidation-reduction processes, coordination complex creation, and free radical formation are examples of these reactions. Surface properties and electrical or crystal structures have a big impact on the reaction mechanism of solid catalysts. Polyfunctional catalysts are solid catalysts that can interact with reactants in more than one way; bifunctional catalysts are widely employed in the petroleum industry for reforming reactions. Many industrial chemical processes rely on catalyzed reactions. Catalyst production is a fast expanding industrial process in itself.
The symbol or formula of the catalyst is written above or below the arrow sign in the equation if the reaction occurs in the presence of a catalyst. The following example will help to clarify this.
Potassium chlorate (KClO3) decomposes into potassium chloride and oxygen gas when heated in the presence of a manganese dioxide catalyst. The following is an example of how this could be expressed:
2KClO3 + Heat → 2KCl + 3O2 (in presence of MnO2)
(Potassium Chlorate) (Potassium chloride) (Oxygen)
The catalyst is MnO2, and the delta (Δ) represents for heat. As a result, the above equation depicts the conditions under which the reaction occurs.
Chemical reaction in Presence of Temperature and Pressure
- Effects of Temperature: The kinetic-molecular theory can be used to describe the influence of temperature and pressure on a liquid. The molecular behaviour of a liquid at a low temperature near its freezing point and a higher temperature near its boiling point varies. Consider how the mobility of atoms or molecules in a liquid is affected by temperature. The particles in a solid, liquid, or gas move faster as the temperature rises. The particles slow down as the temperature drops.
- When a liquid is sufficiently chilled, it solidifies.
- When a liquid is sufficiently heated, it turns into a gas.
- Effects of Pressure: The volume of a liquid is unaffected by changes in pressure. Since any increase in pressure can only slightly reduce the distance between the closely packed molecules, liquids are generally incompressible.
- When the pressure above a liquid is raised high enough, the liquid solidifies.
- When the pressure above a liquid is sufficiently reduced, the liquid transforms into a gas.
The temperature and pressure conditions under which the reaction occurs can also be expressed in an equation by placing their values above or below the arrow sign. The following example will demonstrate this.
Carbon monoxide and hydrogen are used to make methanol or methyl alcohol. The carbon monoxide and hydrogen gas mixture is compressed to 300 atmospheres pressure and then passes over a catalyst made up of zinc oxide and chromium oxide mixture heated to 3000C. The reaction requires a pressure of 300 atmospheres (written as 300 atm), a temperature of 3000C, and a catalyst made up of zinc oxide and chromium oxide (ZnO+CrO3). We may now write down a chemical equation for the methanol generation reaction, along with the conditions, as follows.
CO + 2H2 → CH3OH (at 300 atm, 3000C, in presence of ZnO+CrO3)
(Carbon Monoxide) (Hydrogen) (Methanol)
The state of matter of a substance is an extrinsic property, meaning it can be influenced by its surroundings. The state of matter is influenced by two physical factors that are, temperature and pressure. Temperature and pressure can both be measured, as well as state changes.
When thermal energy is applied to a substance, the temperature rises, changing the state of the substance from solid to liquid (melting), liquid to gas (vaporization), or solid to gas (sublimation). When energy is lost from a substance, the temperature drops, causing it to change from liquid to solid (freezing), gas to solid (deposition), or gas to liquid (condensation). When the pressure applied to a substance increases, the substance can condense. It can vaporize if the pressure is reduced.
What are the conditions for the reaction of photosynthesis?
Photosynthesis is the process through which green plants produce food. During photosynthesis, carbon dioxide reacts with water in the presence of ‘sunlight,’ and the green pigment ‘chlorophyll,’ found in leaves, produces food such as glucose and releases oxygen gas. The existence of sunlight and chlorophyll are required for the photosynthesis reaction to occur. As a result, we may write the following chemical equation for photosynthesis, complete with conditions.
6CO2 + 6H2O → C6H12O6 + 6O2 (in presence of sunlight and chlorophyll)
(Carbon dioxide) (Water) (Glucose) (Oxygen)
Question 1: How does the temperature change affect the particles of matter?
The particles in a solid, liquid, or gas move faster as the temperature rises, and when the temperature drops, the particles slow down.
Question 2: Give an example of a chemical reaction having a temperature change.
A change in temperature is obtained when quick lime is added to water to form slaked lime as it reacts vigorously and produces heat.
Question 3: Is melting of candle wax on heating a chemical reaction or not?
No, the melting of candle wax on heating is not a chemical reaction because, on heating, wax changes its physical state, but there is no change in its properties.
Question 4: How does pressure change the state of a liquid?
When the pressure above a liquid is raised high, the liquid solidifies, and when the pressure above a liquid is reduced, the liquid transforms into a gas.
Question 5: What is a solution made in water called and how is it indicated?
A solution made in water is called an aqueous solution and it is indicated by aq.
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