Chemical Reaction

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<<–2/”>a >a href=”https://exam.pscnotes.com/the-rate-of-a-chemical-reaction/”>The Rate of a Chemical Reaction can be defined as the amount of the reaction which occurs in unit time. The rate of a reaction is measured by choosing certain properties of the reaction which will indicate how far the reaction has gone, and whose magnitude can be observed with time without disturbing the reaction.

For example, a reaction which shows color change: the rate of such reaction can be measured by observing how the intensity of color formed changes with time. In a similar way, a reaction which involves gases can have its rate measured by collecting the gas and observing the way its volume or mass increases with time. Note: increase in rate of reaction corresponds to decrease in time taken for the reaction, and vice versa.

I.e., rate of reaction is inversely proportional to time,

R α1/T

Factors which affect the Rate of Chemical Reactions

Factors which can affect the rate of a chemical reaction include:

  1. Temperature

By the kinetic theory, chemical reactions occur due to collisions of Molecules, atoms or ions involved in the reaction. When the temperature of a reacting system is increased by way of heating, the reacting particles gain energy and are able to move faster, resulting in increased collisions, which increases the rate of the reaction.

An illustration of this can be found in the reaction between sodium trioxo sulphur sulphate(VI) solution and hydrochloric acid. The reaction leads to the Precipitation of sulphur.

By observing the precipitation of sulphur at various temperatures with time, the result obtainable would indicate that: as the temperature of the reaction is increased, the time taken to precipitate sulphur is decreased (i.e. rate of reaction increases).

Note: the way by which the intensity of the precipitate can be measured is to carry out the entire reaction in a beaker, and by placing the beaker and its contents on a white piece of paper with a cross marked on it. The time for the disappearance of the cross when the contents of the beaker are viewed from above will give a measure of the time taken for a certain fraction of the reaction to occur (i.e. the rate of the reaction) – a stop clock or a watch is used to note this time.

By plotting the graph of temperature over time of reaction, we obtain the curve:

Note: the curve slopes from left to right indicating that increase in temperature leads to decrease in time (i.e., increase in rate of reaction) and vice versa. Thus, temperature is inversely proportional to time (Temp α 1/Time).

In general, increase in temperature of a reaction by 100 results in doubly the rate of reaction (i.e. decrease in time taken by half).

  1. Concentration of Reactants

The concentration or density of reacting substances affect their closeness to one another, and consequently the frequency of their collision – this ultimately affects the rate of reaction. The higher the concentration of reactants, the greater the rate of reaction and vice-versa.

To investigate the effect of concentration on the rate of reaction, the reaction between dilute HCl and sodium trioxo sulphur sulphate (VI) solution to precipitate sulphur may be studied.

By observing the reactions of different concentrations of sodium trioxo sulphur sulphate(VI) with fixed concentration of HCl, it would be observed, from the result of the reaction that the higher the concentration, the shorter will be the time taken for sulphur to precipitate, i.e., the higher the concentration, the greater the rate of reaction.

To observe the intensity of sulphur produced at any given moment (this represents the extent of the reaction, i.e. the rate of the reaction), the reaction is carried out in a beaker, placed on a piece of paper with a cross marked on it. The time taken for the cross to be invisible when the content of the beaker is viewed from above is noted using a stop clock or a watch – this is the time taken for a certain fraction of the reaction to occur.

By plotting the graph of concentration against time of reaction, the following curve is obtained:

The curve indicates concentration varying inversely with time, i.e., conc. α 1/T. Hence, increasing the concentration of reacting masses leads to decrease in time of reaction (i.e. increase in rate of reaction). Decreasing the concentration of reacting masses leads to increase in the time of reaction (i.e. decrease in rate of reaction).

Another study to show the effect of concentration of reactants on the rate of reaction is “the iodine-clock reaction” – this is the reaction between hydrogen peroxide solution and acidified potassium iodide solution. Iodine is produced and is indicated by the observation of a dark-blue coloration with starch.

2I–(aq),+ 2H+(aq) + H2O2(aq) → 2H2O (l) + I2(aq)

The procedure is to use a fixed concentration of one reactant together with a variable concentration of the other, and to observe the rate of reaction in each combination.

The result of the study would show that the rate of reaction increases with increase in concentration of the reactants. For gaseous reactions, increase of pressure implies increase of concentration – the rate of the reaction tends to increase as a result of increase in collisions.

Note: generally, increase in the concentration (in moles per dm3 or mmHg for gases) of reactants will result in increase in rate of reaction – i.e. decrease in reaction time – and vice versa. The graph above applies to all similar cases.

  1. Surface Area of Reactants

In heterogeneous reactions – reactions in which all the reactants are not in the same phase (i.e. different states) – the surface area of the reactants have been found to affect the rate of the reactions. For example, comparing the rate of reactions of:

(i) Dilute HCl and marble chips.

(ii) Dilute HCl and powdered marble of the same mass as

(i). CaCO3(s) + 2HCl(aq → CaCl2(aq) + CO2(s) + H2O

(l) Both reactions produce CO2 gas. This causes a reduction in the mass of the reacting vessel with time, and this may be taken as a measure of the rate of the reaction.

The result of both reactions would show that the rate of reaction of the powdered marble is greater than that of the chip (as shown in the graph below – the mass of the reacting vessel of the powdered marble reduces at shorter time than the mass of the reacting vessel of the lump of marble).

The reason for this is that the surface area of the powdered marble, being very large compared with that of the chip is responsible for the difference in their reaction rates.

The graph of the mass of reacting vessel against time of reaction is similar to the diagram below:

Note: The two curves level off at the same point. The reason for this is that the chip (or large piece) completely dissolves after some time, then the rate of its reaction becomes equal to that of the powdered one.

In general, for heterogeneous reactions, reactants of large surface areas have greater rates of reaction (i.e., reactions occur at shorter time) than reactants of small surface areas. The surface area of powder is greater than that of lumps or large piece.

Another way the rates of the above reactions can be measured is to measure their increasing volume of CO2 produced with time. The graph of volume of CO2 produced against time will give:

  1. The Use of Catalyst

The presence of catalysts in chemical reactions would increase their rate.

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A chemical reaction is a process that changes one or more substances into one or more new substances. Chemical reactions are the basis of all chemical change, and they are essential for life.

There are many different types of chemical reactions, but they can all be classified into two main categories: reversible and irreversible. Reversible reactions are those that can go in both directions, while irreversible reactions are those that can only go in one direction.

Reversible reactions are important because they allow for the equilibrium of a system to be maintained. Equilibrium is a state of balance in which the forward and reverse reactions are occurring at the same rate. If the forward reaction is favored, the concentration of the products will increase. If the reverse reaction is favored, the concentration of the reactants will increase. However, if the reaction is at equilibrium, the concentrations of the reactants and products will remain constant.

Irreversible reactions are important because they allow for the formation of new substances. When an irreversible reaction occurs, the reactants are converted into products and cannot be recovered. This is why irreversible reactions are often used in industrial processes.

There are many different factors that can affect the rate of a chemical reaction. These factors include temperature, concentration, pressure, and the presence of a catalyst.

Temperature is one of the most important factors that affects the rate of a chemical reaction. In general, the rate of a reaction increases as the temperature increases. This is because the molecules have more energy at higher temperatures, and they are therefore more likely to collide with each other and react.

Concentration is another important factor that affects the rate of a chemical reaction. In general, the rate of a reaction increases as the concentration of the reactants increases. This is because there are more molecules of the reactants present in a higher concentration, and they are therefore more likely to collide with each other and react.

Pressure is also a factor that can affect the rate of a chemical reaction. In general, the rate of a reaction increases as the pressure increases. This is because the molecules are forced closer together at higher pressures, and they are therefore more likely to collide with each other and react.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed by the reaction. Catalysts work by providing an alternative pathway for the reaction to occur. This pathway may be lower in energy than the uncatalyzed pathway, and it may therefore be more likely to occur.

Chemical reactions are essential for life. They are responsible for the production of food, the release of energy, and the removal of waste products. Chemical reactions are also responsible for the formation of new substances, such as proteins and DNA.

Chemical reactions are a fascinating and complex topic. There are many different types of chemical reactions, and they can be affected by a variety of factors. Chemical reactions are essential for life, and they are responsible for the production of food, the release of energy, and the removal of waste products.

1. What is a chemical reaction?

A chemical reaction is a process that changes one or more substances into new substances.

2. What are the types of chemical reactions?

There are many different types of chemical reactions, but some of the most common include:

  • Synthesis reactions: These reactions combine two or more substances to form a new substance.
  • Decomposition reactions: These reactions break down a substance into two or more simpler substances.
  • Single replacement reactions: These reactions replace one element in a compound with another element.
  • Double replacement reactions: These reactions exchange ions between two compounds.
  • Combustion reactions: These reactions combine a substance with Oxygen to produce heat and Light.

3. What are the steps in a chemical reaction?

The steps in a chemical reaction are:

  1. The reactants collide with each other.
  2. The reactants form an activated complex.
  3. The activated complex breaks down into the products.

4. What are the factors that affect the rate of a chemical reaction?

The factors that affect the rate of a chemical reaction include:

  • The concentration of the reactants: The higher the concentration of the reactants, the faster the reaction will occur.
  • The temperature: The higher the temperature, the faster the reaction will occur.
  • The presence of a catalyst: A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed by the reaction.

5. What are the products of a chemical reaction?

The products of a chemical reaction are the substances that are formed when the reactants react.

6. What is the law of conservation of mass?

The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction.

7. What is the law of conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another.

8. What is a chemical equation?

A chemical equation is a way of representing a chemical reaction using symbols and formulas.

9. What is a balanced chemical equation?

A balanced chemical equation is a chemical equation in which the number of atoms of each element is the same on both sides of the equation.

10. What is a mole?

A mole is a unit of measurement that is used to measure the amount of a substance. One mole is equal to 6.022 x 10^23 atoms or molecules of a substance.

11. What is the molar mass of a substance?

The molar mass of a substance is the mass of one mole of that substance. It is calculated by multiplying the atomic mass of each element in the substance by the number of atoms of that element in the substance and then adding the products together.

12. What is the mole fraction of a substance?

The mole fraction of a substance is the ratio of the number of moles of that substance to the total number of moles of all the substances in a mixture.

13. What is the percent composition of a substance?

The percent composition of a substance is the Percentage of that substance in a mixture. It is calculated by multiplying the mole fraction of the substance by 100%.

14. What is the empirical formula of a compound?

The empirical formula of a compound is the simplest whole-number ratio of the atoms of each element in the compound.

15. What is the molecular formula of a compound?

The molecular formula of a compound is the actual number of atoms of each element in the compound.

16. What is a chemical bond?

A chemical bond is the force that holds atoms together in a molecule.

17. What are the different types of chemical Bonds?

The different types of chemical bonds include:

  • Ionic bonds: Ionic bonds are formed when one atom donates an electron to another atom.
  • Covalent bonds: Covalent bonds are formed when atoms share electrons.
  • Metallic bonds: Metallic bonds are formed when atoms share electrons in a sea of electrons.
  • Hydrogen bonds: Hydrogen bonds are weak bonds that form between hydrogen atoms and electronegative atoms.

18. What is a chemical equilibrium?

A chemical equilibrium is a state of balance in which the rate of the forward reaction is equal to the rate of the reverse reaction.

19. What is Le Châtelier’s principle?

Le Châtelier’s principle states that if a Stress is applied to a system at equilibrium, the system will shift in a way that relieves the stress

Sure, here are some MCQs without mentioning the topic Chemical Reaction:

  1. Which of the following is not a type of chemical reaction?
    (A) Synthesis
    (B) Decomposition
    (C) Combustion
    (D) Nuclear fission

  2. In a chemical reaction, the reactants are converted into products. Which of the following is not a reactant in the reaction $2H_2 + O_2 \to 2H_2O$?
    (A) Hydrogen
    (B) Oxygen
    (C) Water
    (D) Heat

  3. The rate of a chemical reaction is affected by several factors, including temperature, concentration, and surface area. Which of the following is not a factor that affects the rate of a chemical reaction?
    (A) Catalyst
    (B) Pressure
    (C) Collision frequency
    (D) Activation energy

  4. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction. Which of the following is not a true statement about catalysts?
    (A) Catalysts can be used to speed up or slow down chemical reactions.
    (B) Catalysts can be used to make chemical reactions more efficient.
    (C) Catalysts can be used to make chemical reactions more selective.
    (D) Catalysts are always consumed in a chemical reaction.

  5. An endothermic reaction is a reaction that absorbs heat from its surroundings. Which of the following is an example of an endothermic reaction?
    (A) The reaction of sodium and chlorine to form sodium chloride
    (B) The reaction of water and carbon dioxide to form carbonic acid
    (C) The reaction of glucose and oxygen to form carbon dioxide and water
    (D) The reaction of ammonium nitrate to form nitrogen gas, water, and oxygen gas

  6. An exothermic reaction is a reaction that releases heat to its surroundings. Which of the following is an example of an exothermic reaction?
    (A) The reaction of sodium and chlorine to form sodium chloride
    (B) The reaction of water and carbon dioxide to form carbonic acid
    (C) The reaction of glucose and oxygen to form carbon dioxide and water
    (D) The reaction of ammonium nitrate to form nitrogen gas, water, and oxygen gas

  7. A chemical equilibrium is a state of balance in which the rate of the forward reaction is equal to the rate of the reverse reaction. Which of the following is not a true statement about chemical equilibrium?
    (A) The concentrations of the reactants and products in a chemical equilibrium are constant.
    (B) The rate of the forward reaction is equal to the rate of the reverse reaction at chemical equilibrium.
    (C) The position of a chemical equilibrium can be shifted by changing the temperature, pressure, or concentration of the reactants or products.
    (D) The equilibrium constant for a chemical reaction is a measure of the relative concentrations of the reactants and products at equilibrium.

  8. A buffer solution is a solution that resists changes in pH when small amounts of acids or bases are added. Which of the following is not a true statement about buffer solutions?
    (A) Buffer solutions contain a weak acid and its conjugate base.
    (B) Buffer solutions contain a weak base and its conjugate acid.
    (C) Buffer solutions can be used to maintain a constant pH in a solution.
    (D) Buffer solutions are always acidic.

  9. A precipitate is a solid that forms when two solutions are mixed. Which of the following is not a true statement about precipitates?
    (A) Precipitates can be formed when two solutions of different salts are mixed.
    (B) Precipitates can be formed when a solution of an acid is mixed with a solution of a base.
    (C) Precipitates can be formed when a solution of a salt is mixed with a solution of a gas.
    (D) Precipitates can be formed when a solution of a salt is mixed with a solution of a non-electrolyte.

  10. A homogeneous mixture is a mixture in which the components are evenly distributed throughout the mixture. Which of the following is not an example of a homogeneous mixture?
    (A) Air
    (B) Water
    (C) Soil
    (D) Salt water