GAMSAT Sample Questions

Unit 7
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Questions 31-35

Enthalpy is the chemical energy stored inside any substance This chemical energy is due to the chemical bonds. In a chemical reaction the existing bonds break and new bonds are formed . Energy is consumed in breaking of bonds and formation of new bonds releases energy. Thus, energy changes take place during chemical reactions.

Thermochemical Equation, a chemical equation, shows the enthalpy change (%u2206H) for a physical or chemical change at given temperature and pressure. The science of the study of the energy changes which take place during chemical reactions is called Thermochemistry

The enthalpy change during reactions is measured by observing energy exchange between the chemicals and the surroundings. There are many types of Enthalpy Changes; for example enthalpy of neutralization . When a strong acid reacts with an alkali , water is formed and the process is called neutralization . Enthalpy of neutralization is constant.
The heat of reaction is the difference between the enthalpies of the reaction products and reactants at constant pressure and temperature. It is the amount of heat evolved or absorbed during the reaction. It is also called Enthalpy of reaction.
%u2206H = Hproducts - Hreactants

If heat is liberated in the reaction, the process is said to be exothermic and heat of reaction is a negative number. An exothermic reaction has a negative %u2206H. If heat is absorbed, the process is endothermic and heat of reaction is a positive number. An endothermic reaction has a positive %u2206H.

In exothermic process, the total enthalpy of products is lower than that of reactants Thus the heat is released and the heat of reaction is indicated by negative value of %u2206H. Hproducts < Hreactants

In endothermic process, the total enthalpy of products is higher than that of reactants Thus the heat is absorbed and the heat of reaction is indicated by positive value of %u2206H. Hproducts > Hreactants

The magnitude of the heat of reaction depends on mass, pressure, volume, temperature and physical states of the substance.

31 Point out wrong answer

A. The heat of reaction is the difference between the enthalpies of the reaction products and reactants at constant pressure and temperature.

B. The Enthalpy of reaction is the amount of heat evolved or absorbed during the reaction. It is also called Enthalpy of reaction.

C. If heat is liberated in a reaction, the process is said to be endothermic.

D. Thermochemical Equation, a chemical equation, shows the enthalpy change for a physical or chemical change.

32 In an exothermic process, the heat of reaction is
A. Negative
B. Positive
C. Zero
D. Constant

33 Heat of neutralization of a strong acid by a strong base is always
A. Different
B. Zero
C. Constant
D. More than zero

34 The heat of reaction does not depend upon
A. Physical states of the substances
B. Amount of the substances
C. Temperature
D. Presence of catalyst

35 Ammonium chloride when dissolve in water leads to cooling sensation. The dissolution of NH4CI at constant temperature is accompanied by
A. Increase in enthalpy
B. Decrease in enthalpy
C. No changes in enthalpy
D. 'a' or 'b'

Unit 7

31. STEP 1 => What do you need to determine to solve the problem?

We need to determine the wrong statement out of five statements

STEP 2 => What relevant data provided in this problem are necessary in order to answer the question? The definition of terms- heat of reaction, enthalpy of reaction, endothermic, and thermochemical equation are given,

STEP 3 => Use the relevant data to solve the question.
If heat is liberated in a reaction, the process is said to be exothermic and not endothermic.

Answer C.

32 STEP 1 => What do you need to determine to solve the problem?
We have examine the heat of reaction is in an exothermic process
STEP 2 => What relevant data provided in this problem are necessary in order to answer the question? The definition of term "an exothermic process" is given

STEP 3 => Use the relevant data to solve the question. If heat is liberated in a reaction, the process is said to be exothermic.

Answer A.

33 STEP 1 => What do you need to determine to solve the problem?
We have to find nature of heat of neutralization.
STEP 2 => What relevant data provided in this problem are necessary in order to answer the question? Heat of neutralization of a strong acid by a strong base is the heat released when 1 mole of water is formed during the neutralization of strong acid by an alkali. It is always constant

STEP 3 => Use the relevant data to solve the question. It is a constant

Answer C.

34 STEP 1 => What do you need to determine to solve the problem?
We have to know factors on which the heat of reaction depends.
STEP 2 => What relevant data provided in this problem are necessary in order to answer the question? The magnitude of the heat of reaction depends on mass, pressure, volume , temperature and physical states of the substance.

STEP 3 => Use the relevant data to solve the question. The heat of reaction does not depend on presence of catalyst.

Answer D.

35 STEP 1 => What do you need to determine to solve the problem?
We have to know factors on which the heat of reaction depends.
STEP 2 => What relevant data provided in this problem are necessary in order to answer the question? Enthalpy of Solution is the enthalpy change when 1 mole of substance is completely dissolved in water. It is given that there is cooling sensation. Heat is absorbed in the reaction.

STEP 3 => Use the relevant data to solve the question. The enthalpy is positive.

Answer A.