Hreaction= Hproduct - Hreactant
Q.1 With the use of a catalyst, which of the following energy values decreases?
(a) Enthalpy of reaction
(b) Heat of reaction
(c) Activation energy
(d) Collision energy
Answer: (c) In the presence of a catalyst, the activation energy for a reaction decreases that increases the rate of reaction.
Q. 2 Why does the enthalpy of reaction signify a negative for exothermic reaction?
Answer: The enthalpy of reaction is the difference in the enthalpy of product and reactant molecules.
Hreaction=Hproduct - Hreactant
For an exothermic reaction, the enthalpy of the product is lesser than reactant as some of the energy is released in the form of heat or light. Thus, the difference that is enthalpy of reaction will be negative.
Q.3 Identify one of the most common exothermic reactions in our surroundings.
(a) Burning of candle
(b) Cooking of food
(c) Distillation of crude oil
(d) Water sedimentation
Answer: (a) Burning of candle is an exothermic reaction as it releases a certain amount of energy in the form of heat and light.
Question 1: What are three examples of endothermic reactions?
Three examples of endothermic reactions are:
Question 2: Is exothermic hot or cold?
Exothermic reactions release a certain amount of energy in the form of heat or light whereas endothermic reactions absorb a certain amount of energy so the temperature of the reaction system decreases whereas it increases during exothermic reactions. So exothermic reactions are hot.
Question 3: What is the difference between an exothermic and endothermic reaction?
|Exothermic reaction||Endothermic reaction|
|It occurs with release of energy||It absorbs some energy.|
|Temperature of the reaction system will increase.||Temperature of the reaction system will decrease.|
|∆H = -ve||∆H = +ve|
Question 4: Do endothermic reactions feel hot or cold?
An endothermic reaction can be defined as the chemical reaction that occurs with absorption of a certain amount of energy in the form of heat. For example; dissolution of salt in water is an endothermic process as it decreases the temperature of the system. So endothermic reactions are cold.