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Chapter 7 Thermochemistry Chemistry 11th Class Punjab Short Questions

Question No. 1 - What is a spontaneous process?

Answer No. 1 - The process which takes place on its own is called spontaneous process. No external. Assistance is required. It moves from non-equilibrium state. It is unidirectional and irreversible.

Question No. 2 - Burning of an candle is a spontaneous process. Justice?

Answer No. 2 - A reaction will also be called spontaneous process if it needs energy to start with.
Burning of candle also a spontaneous process which needs energy to start.Once the candle is made to lit with match spark.It continues to burn afterword.
Therefore burning of candle is a spontaneous process.

Question No. 3 - How the temperature of the system change during exothermic and endothermic reactions?

Answer No. 3 - In an exothermic reaction, heat is evolved which increases the temperature of the system. In an endothermic reaction, heat is absorbed, so the temperature of the system falls down. These statements are true when the system is isolated.

Question No. 4 - What is meant by heat(q) and work (W) in thermochemistry?

Answer No. 4 - There are two fundamental ways of transferring energy to or from a system. These are heat and work. Heat is not a property of a system. It is therefore not a state functions. Heat evolved or absorbed by the system is represented by a symbolq.Work is also a form in which energy is transferred from one system to another.

Question No. 5 - Acid-base neutralization process is always exothermic.Give reasons?

Answer No. 5 - The standard enthalpy of neutralization is the amount of heat evolved when one mole of hydrogen icons H+From an acid, react with one mole of hydroxide ions from a base to form one mole of water. For example, the enthalpy of neutralization of sodium hydroxide by hydrochloric acid is -57.4 kjmol-1
Thus heat is evolved in acid base neutralization process is always exothermic.

Question No. 6 - Define Born-Haber cycle and lattice energy?

Answer No. 6 - Born-Haber cycle: The sum of energy changes for a closed cyclic process is zero, If the initial and final states are same.
Lattice Energy: The amount of energy released when gaseous icons of opposite charges combine to give one mole of a crystalline ionic compound.

Question No. 7 - Define Thermochemistry.

Answer No. 7 - That branch of chemistry which deals with the heat energy changes along with the phase changes and occurring of the chemical reactions, is called thermochemistry.

Question No. 8 - Enthalpy is a state function Justify?

Answer No. 8 - The total heat content of a system is called enthalpy. Equation
H=E+PV E,P and V are state functions so enthalpy is also a state function. It is not possible to measure the enthalpy of a system in a given state.However change in enthalpy can be measured for a change in the state of system.

Question No. 9 - Described System and Surrounding?

Answer No. 9 - System: The part of universe which is under your observation is called system.
Surrounding: Everything that is not a part of system is called surrounding,e.g. Water in a glass is a system and all around is surrounding.

Question No. 10 - Spontaneous reaction always proceed in the forward direction. Give reason?

Answer No. 10 - Spontaneous process are unidirectional, irreversible and real processes. These can take place without any external assistance. That's why reactions always proceed in forward direction.

Question No. 11 - Is it true that a non-spontaneous process never happen in universe? Explain it?

Answer No. 11 - Yes it is true that non-spontaneous processes never happen in the universe. Because a non-spontaneous process needs energy to take place.Since this energy is not available of its own. Therefore a non-spontaneous process never happens in the universe.

Question No. 12 - What is state and state function?

Answer No. 12 - The condition of a system is called the state of a system. The initial state is a description before a change happens. Final state is a description after a change takes place. State function is the macroscopic property of a system, which has some definite values for initial and final states and is independent of the path which is adopted to bring out the change.

Question No. 13 - What are thermochemical reaction, give their type.

Answer No. 13 - Thermochemical Reaction: Those reaction in which energy is either evolve or absorbed during a chemical change is called thermochemical reactions.
Two types of those reactions:
1. Exothermic reactions
2. Endothermic reactions

Question No. 14 - Why in exothermic reaction, heat is released from the system?

Answer No. 14 - In a chemical change if enthalpy of product is less than the enthalpy of reactant.Heat is released from the system to surrounding . Hence heat is released in an exothermic reaction.

Question No. 15 - Differentiate between law of conservation of energy and Hess's law?

Answer No. 15 - Energy can neither be created nor destroyed, can be changed from one form to another is called Law of Conservation of Energy.
If a chemical change takes place by several different routes, the overall energy change is the same, regardless of the route by which the chemical change occurs, provided the initial and final conditions are the same is known as Hess"s Law.

Chapter 7 Thermochemistry Chemistry 11th Class Punjab Short Questions

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