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Rate of change:

 

The rate of change or reaction rate is the measure of the change in concentration of the reactants or the products per unit time. 
Rate=concentration/time

 

Rate of change Sample Questions:

 

 

Question 1: A foreign substance that increases the speed of a chemical reaction is called-

 

(a) Promotor
(b) Catalyst
(c) Moderator
(d) Inhibitor

 

Answer: Option b) Catalyst
Explanation: Catalyst are the Substances which alter the rate of a chemical reaction and remain chemically and quantitatively unchanged themselves.

 

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Question 2: Instantaneous reaction rate is-

 

(a) Rate at particular moment of time
(b) Pressure at particular time
(c) Average rate of the reaction
(d) Concentration at particular time

 

Answer: Option a) Rate at particular moment of time

Explanation: The instantaneous rate is the rate of a chemical reaction at any particular point of time, this period of time is so short that the concentrations of reactants and products change only by a negligible amount.

 

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Question 3: The term  -dx/dt  in the rate expression refers to the-

 

(a) Increase in concentration of the reactants
(b) Average rate of the reaction
(c) Instantaneous rate of the reaction
(d) Concentration of the reactants

 

Answer: Option c) Instantaneous rate of the reaction

Explanation: -dx/dt in rate expression refers to the instantaneous rate of the reaction.
It is the ratio of the decrease in the concentration of a reaction to the time taken for this decrease.

 

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Question 4: The rate of a chemical reaction gives information about-

 

(a) The reactants participating in the reaction
(b) The products formed in the reaction
(c) How slow or fast the reaction is taking place
(d) None of the above

 

Answer: Option c) how slow or fast the reaction is taking place

Explanation: The rate of a chemical reaction is the speed at which reactants are getting converted into products. In other words it tells us how fast or slow a reaction is.

 

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Question 5: A catalyst alters, which of the following in a chemical reaction?

 

(a) Entropy
(b) Enthalpy
(c) Internal energy
(d) Activation energy

 

Answer: Option d) Activation energy

Explanation: Adding a catalyst to a chemical reaction alters the activation energy. The catalyst provides an alternate pathway of lower activation energy, and therefore increasing the rate of reaction.

 

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Question 6: Which of the following factors affect the chemical reaction-

 

(a) Surface area
(b) Temperature
(c) Concentration
(d) All of the above

 

Answer: Option d) All of the above.

Explanation: The rate of a chemical reaction is affected by a number of factors. For example- By increasing the surface area of a solid reactant, by increasing or decreasing the temperature of reactants and by increasing the concentration.

 

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Question 7: Enzyme are biological-

 

(a) Substrate
(b) Products
(c) Catalysts
(d) None of the above

 

Answer: Option c) Catalysts

Explanation: Enzymes are the biological catalysts that catalyses the reaction happening inside living bodies. They speed up the reaction by lowering the activation energy.

 

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Question 8: Spontaneous reaction doesn't have an activation energy

 

(a) True
(b) False
 

Answer: Option b) False

Explanation: All reactions including spontaneous reactions have activation energy. When activation energy is large, reaction occurs slowly and when its small reaction occurs rapidly.

 

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Question 9: In exothermic reaction the heat is- 

 

(a) Released
(b) Absorbed
 

Answer: Option a) Released

Explanation: Exothermic reactions are those reactions in which energy is released in the form of heat. Endothermic reactions involve reactions where heat is absorbed.

 

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Question 10: For reactions that do not involve gases the rate is not dependent on-

 

(a) Pressure
(b) Temperature
(c) Concentration
(d) Catalyst

 

Answer: Option a) Pressure

Explanation: Out of three states of matter, gases are the only one that exert pressure. Therefore reactions not involving gases are independent on pressure.

 

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Frequently Asked Questions

 

 

How to find the rate of change?

 

The rate of change or reaction rate is the measure of the change in concentration of the reactants or the products per unit time. 


Rate=concentration/time


The rate can be expressed as the rate of disappearance of reactants as well as the rate of formation of products.

 

 

What is the rate of change in simple definition?

 

The rate of change is the change of concentration over the change in time. It can be expressed in following two ways- 

 

The Rate of Disappearance of Reactants.

 

The Rate of Formation of Products.

 


What does the difference in the rate of change mean?

 

The rate of a reaction changes during the course of a chemical reaction. The difference in rate of a chemical reaction at two different points of time is called the rate of change.
 

 

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