UNIT#08 THERMOCHEMSITRY AND ENERGETICS OF CHEMICAL REACTIONS Flashcards
Thermodynamics does NOT deal with:
➡Heat of Reaction❌
➡Rate of Reaction✅
➡Spontaneity of Reaction❌
➡Entropy of Reaction❌
If an endothermic reaction is allowed to take place very rapidly in air, the temperature of the surrounding air will:
Decrease
The exothermic process is;
Respiration
A process, which takes place on its own without any outside assistance, is termed as:
Spontaneous
The work done by expansion of gas against constant pressure is:
-PΔV
(Work done by the system is considered negative)
A state function which describes together the internal energy and product of pressure and volume is called:
Enthalpy
The enthalpy of formation of a compound is:
Either positive or negative
Enthalpy is an expression for the:
Heat Energy
Which one of the following has a standard enthalpy of formation that is zero?
Cu (s)
➡Standard Enthalpy of an element in its standard state is zero
Which of the following statement is correct:
➡ΔH is positive for exothermic reaction❌
➡ΔH is negative for endothermic reaction❌
➡The heat of neutralization of strong acid with a strong base is always the same✅
➡The enthalpy of fusion is negative❌
What is not correct about ΔHf :
➡Its value gives an idea about the relative stability of reactants and the products❌
➡It is always negative❌
➡Value depends upon the nature of bonds✅
➡ITs value may be negative or positive❌
Which of the following has a positive value of enthalpy:
Atomization
NaOH + HCl ➡ NaCl + H2O
Enthalpy change in the above reaction is called:
Enthalpy of neutralization
Enthalpy o neutralization per mole of H2SO4/Ba(OH)2 is:
-54.7 kJmol-1
Which of the following processes has always ΔH= -ve
Combustion
Heat absorbed or evolved during the chemical reaction at constant pressure is:
ΔH
The change in enthalpy of a system when one mole of the substance is completely burnt in air or oxygen is called:
Heat of combustion
Which of the following enthalpy change may be positive or negative value:
➡ΔHc
➡ΔHsolution
Neutralization of acid-base is:
➡Spontaneous
➡Exothermic
ΔH represent the enthalpy change at;
25°C and 1 atm pressure
The enthalpy changes ΔH of a process are given by the relation:
ΔE = ΔH + PΔV
A system absorbs 100kJ heat and performs 50kJ work on the surroundings. The change in internal energy of the system is:
50kJ
Which equation represents the atomization of iodine:
1/2 I2(s) ➡ I(l)
The ΔH of a reaction is recorded at:
298K
Which of the following enthalpies is always negative;
Enthalpy of neutralization
Which of the following enthalpies is always positive:
Enthalpy of sublimation
Enthalpy of reaction can be measured in;
Glass calorimeter
How much heat is evolved by 100g of water when its temperature decreases from 25°C to 5°C?
-84,00J
(q = msΔT)
➡Specific Heat o water is 4.2 J/gK
Enthalpy of combustion of food, fuel and other compounds can be measured accurately by
Bomb Calorimeter
Which enthalpy of reaction can not be determined by glass calorimeter
Enthalpy of combustion
Total Heat energy (q) can be calculated in a bomb calorimeter by using the following:
c x ΔT
(q = c x ΔT)
Which one of the following is applied to calculate lattice energy indirectly?
Born-Haber cycle
In order to determine ΔHlattice of ionic compound which is the correct relationship?
ΔHlattice = ΔHf - ΔHx
Which equation shows the lattice energy of an ionic compound?
ΔH (lattice) = Hf - Hx
With the increase in charge to size ratio of ions, the lattice energy:
Increases
(ΔHlattice ∝ Charge/Size of an atom)
Hess’s law is analogous to;
Law of heat summation
Which of the following enthalpies of formation cannot be measured directly?
➡ΔH lattice for the ionic compound
➡ΔH for CO
➡ΔH for B2O3
The standard enthalpy changes of formation of carbon dioxide and water are -394kJmol-1 and -286kJmol-1 respectively, if the standard enthalpy change of combustion of propyne, C3H4 is -1932kJmol-1. What is the standard enthalpy change of formation?
-184 kJmol-1
The heat of combustion o ethane (C2H6) is -337.0 kcal at 25°C. The heat reaction when 3g of ethane is burnt completely is:
-33.7 kcal
Hess’s law is known as:
Law of heat summation
Relation between qp and qv:
qp > qv
The formation of SO3 from SO2 is ___ reaction.
Endothermic
For strong acid and strong base neutralization energy:
Constant
Unit of energy:
➡Joule
➡Kilojoule
➡Calorie
The unavailability of methods to find out the heat of reactions accurately makes thermochemistry
A limited field of study
Which one of the following is not an example of a state function?
Heat (q)
Temperature and volume in an experiment are part of :
State of a system
In endothermic reaction heat is absorbed from:
Surrounding
ΔH for the exothermic reaction is:
Negative
Which of the following condition is constant in the bomb calorimeter;
Volume
Heat exchanged between the system and surrounding at constant volume is shown by the relation
ΔH = qv + w
At constant volume, the heat supplied is equal to:
Internal energy change
Work done on the system is:
Positive
Which one is not a state function:
Work
Heat supplied at constant pressure equals:
Enthalpy
Enthalpy is the sum of the internal energy and:
Work done
Heat o a solution for the substance whose solubility decreases with an increase in temperature is:
Negative
Enthalpy change of solution of Na2CO2 is a ____ reaction
Exothermic reaction
An enthalpy cycle used to calculate the lattice energy is;
Born Haber cycle
Energy for the endothermic reaction is given a ___ value:
Positive
Which is correct for 1st law of thermodynamics?
ΔE = q +W
The energy of products is greater in:
Endothermic Reaction
Amount of heat absorbed by 2kg of water when temperature changes by 10°C are:
84,000
(q = msΔT)
When a bond is formed, energy is;
Released
Which one is the state function?
PTVUHSG
What is the value of one calorie in Joule?
4.18J
The formation of carbon dioxide hinders calculating the heat of formation of;
CO
Decomposition of water into hydrogen and oxygen is a:
Endothermic Reaction
The heat of the formation of CO
-110 kJ/mol
When 40J heat is provided and 20J work is done, if the initial energy is 10J then the final internal energy is;
30J
In glass calorimeter, which is constant
Pressure
A spontaneous process is;
➡Unidirectional and Irreversible
➡Unidirectional and Real
➡Irreversible and Real
ΔH will be given a negative sign in:
Exothermic Reaction
Reactants have high energy than products;
Exothermic Reaction
The reaction of water with quick lime results in a rise in the temperature of the system. Using the concentration change, indicate the nature of reaction.
Exothermic Reaction
Which of the following enthalpy change is always exothermic?
Enthalpy of Combustion
The heat of formation of MgO is given below.
Mg + 1/2 O2 ➡MgO ΔH=-692 kJ/mol. This equation shows that:
The product is very stable
When one mole of gaseous hydrogen ions are dissolved in water to form an infinitely dilute solution, the amount of heat liberated is;
-1075 kJ/mol
In standard enthalpy of atomization heat of surrounding:
Decreases
The heat of formation (ΔH) for CO2 is;
-394 kJ/mol
2H2 + O2 ➡2H2O ΔH=205.5 kJ/mol
What will be the enthalpy change in the above reaction:
-205.5 kJ/mol
1/2 H2(g) ➡ H(g) ΔH=218 kJ/mol
In this reaction ΔH will be called:
Enthalpy of atomization
Determine the value of enthalpy of formation of NH4Cl:
-692 kJmol-1
Enthalpy is measured at:
298K and 1 atm
When two moles of H2 and one mole of O2 react to form H2O 484 KJ heat is evolved what is ΔHf for one mole of H2O
-242 KJmol-1
The lattice energy of an ionic crystal is the enthalpy of
Formation
The thermal energy at constant pressure is called:
Enthalpy
The born-Haber cycle is used to determine the lattice energies of;
Ionic Solids
One calorie is equal to;
4.18J
The net change in energy in a chemical reaction is the same whether it takes place directly or indirectly. It is called:
Hess’s Law
The enthalpy of formation of an ionic compound is -392kJ/mol. Total energy changes (ΔHx) involved in the formation of gaseous ions from normal physical state is 280kJ/mol. The enthalpy of lattice is:
-672 kJ/mol
Enthalpy of neutralization of strong acids and bases is same because:
H+ and OH- combine to form H2O
Unit of heat is SI system is:
J
If there is the interconversion of solid and liquid states then:
➡ΔV = 0
➡ΔH = ΔE
First law of thermodynamics relates:
➡Internal Energy
➡Heat
➡Work
An exothermic process is:
O (g) + 1e- ➡O-1
If an endothermic reaction is allowed to take place very rapidly in air the temperature of the surrounding air:
Decreases
Which of the following sets constitutes of all the state functions of system:
➡Enthalpy
➡Entropy
➡Internal Energy
___ is not a state function.
Heat
Which of the following enthalpy change (ΔH) is always endothermic
ΔH (atomization)
Incorrect statement about endothermic reaction is;
➡Evaporation is an endothermic process❌
➡Products are more stable than reactants✅
➡ΔH is positive❌
➡Reaction mixture becomes stable❌
Among the following changes, which is exothermic?
➡Freezing
➡Condensation
➡Combustion
Which of the following process will be spontaneous and endothermic:
➡Melting of ice
➡Evaporation of water
➡Dissolution of NH4Cl
When water is added to quicklime, the reaction is:
Explosive
Which is non-spontaneous reaction?
N2 + O2 ➡2NO
The sum of all the energies of atoms, molecules or ions within a system is called:
Internal Energy
Which statement is true when liquid is converted into vapors?
Heat is absorbed
When ΔE of a system increases, then which of the following possibilities is correct?
➡Temperature of the system can increase
➡Phase change may take place
➡Chemical reaction can occur
ΔH = ΔE for which of the following reaction
K + H2O ➡ KOH + H2
According to the first law of thermodynamics, energy from the system to the surrounding can be transferred in the form of:
Heat and Work
Change in enthalpy of ΔH of a gaseous system can be calculated by following relationship:
ΔH = ΔE + PΔV
The amount of heat evolved when one mole of CH3COOH reacts with one mole of NaOH is:
< 57.4 kJ
Standard enthalpies of formation of O3, CO2, NH3 and HI are 142.2, -33.3, -46.2 and +25.9 kJ/mol respectively. The order o their increasing stabilities will be:
O3, HI, NH3, CO2
The enthalpy change for the reaction C(s) + O2(g) ➡ CO2 is called:
➡Enthalpy of formation
➡Enthalpy of combustions
➡Enthalpy of reaction
Which of the following processes has always ΔH = -ve
Combustion
Which one of the following reactions represents both standard enthalpy of combustion as well as standard enthalpy of formation
C (s) + O2 ➡ CO2(g)
The enthalpy of atomization of H2 is 218kJ/mole, the enthalpy of formation of H2 from gaseous atoms:
-218 kJ/mole
Which reaction shows enthalpy of formation:
C + O2 ➡CO2
The enthalpy of formation of an ionic compound is -392 kJ/mol. Total energy changes involved in the formation of gaseous ions form normal physical state is 280 kJ/mol. The enthalpy of lattice is:
-672 kJ/mol
Which of the following change in enthalpy in Born-Haber cycle may be negative
H (E.A)
Hess Law follows:
➡First law of thermodynamics
➡Law of conservation of energy
The net heat change in a chemical reaction is the same whether it is brought about in two or more different ways in one or several steps. It is known as:
Hess’s Law
Standard heat of formation of Al2O3 cannot be determined directly because:
Protective layer of Al2O3 form
One joule is equivalent to:
1/4.184 Cal
The enthalpies of all elements in their standard states are;
Zero
____ is not a state function.
Heat
No work is done at constant:
V
For an endothermic reaction, enthalpy of reactants:
Is smaller than that of the products
Most of the reactions which give stable products are;
Exothermic
Decomposition of H2O is;
Endothermic reaction
What type of reaction constitutes a limiting case between spontaneous and non-spontaneous reactions:
Reversible Reaction
In an endothermic reaction:
Er < Ep
In an exothermic reaction the heat energy is ______ while in an endothermic reaction it is;
➡Released
➡Absorbed
Whenever a reaction is endothermic, then it means that:
Heat is transferred from the surroundings to the system
Enthalpy of neutralization of strong acids and strong bases have the same values because;
The net change involves the combination of H+ and OH- ions to form water
The measurement of enthalpy change at standard conditions means that we should manage the measurement at:
25°C at 1 atm
The enthalpy change for the reaction C2H2 + 5/2 O2 ➡2CO2 + H2O is known as enthalpy of:
Enthalpy of Combustion
BaCl2 + H2SO4 ➡ BaSO4 + HCl, an exothermic reaction, the heat change represented by the above equation is called;
Heat of Reaction
The enthalpy of atomization of H2 is 218 kJ/mol and the enthalpy of formation of H2 from gaseous atoms
-436 kJ/mol
An enthalpy change which is always exothermic:
ΔHn
(Enthalpy of Neutralization)
The enthalpy change for the reaction, C2H5OH + 3O2 ➡ 2CO2 + 3H2O is known as enthalpy of;
Combustion of C2H5Oh
Which of the following gases have the highest heat of combustion
Acetylene
Which one of the following pairs has a maximum enthalpy of neutralization;
HCl + NaOH
ΔH of a system can be calculated by which of the following relationship
q = m x s x ΔT
Bomb calorimeter is used to determine the;
ΔHc
What is the unit of molar heat capacity?
J/mol¹K¹
This is true about the lattice energy of an ionic compound
➡Cannpt be determined directly
➡Can be obtained by means of the Born Haber cycle
The enthalpy of formation of an ionic compound is -392 kJ/mol. Total energy changes (ΔHx) involved in the formation of gaseous ions from a normal physical state is 280 kJ/mol. The enthalpy of the lattice is;
-672 kJ/mol
Choose from the following the correct statement about the Born Haber cycle
The lattice energy of crystalline substances can be calculated easily
Standard heat of formation of Al2O3 cannot be determined directly because:
A protective layer of Al2O3
The heat of combustion of graphite at 25°C is -393.51 kJ/ mol and that of a diamond is -395.41 kJ/mol. What is the enthalpy for the conversion of graphite into diamond at the same temperature?
+1.9 kJ/mol
By applying Hess’s Law, we can calculate:
ΔH
Enthalpy of neutralization of strong acids and strong bases have the same values because:
The net change involves the combination of H+ and OH- ions to form water.
For an endothermic reaction, enthalpy of reactants
Is smaller than that of the products
Which of the following has a positive value of enthalpy
Atomization
The net heat change in a chemical reaction is the same whether it is brought about in two or more different ways in one or several steps. It is known as;
Hess’s Law
Hess’s Law is analogous to;
Law of Heat summation
NaOH + HCl ➡NaCl + H2O. Enthalpy change in the above reaction is called;
ΔH = ΔE
A calorie is equivalent to:
4.184 J
The values of ΔH for the process I + e ➡ I-1 are;
< O
The enthalpy of formation of a compound is;
Either Positive or Negative
What is correct about the heat of combustion:
It is always negative
What is not correct about ΔHf:
It is always negative
If an endothermic reaction is allowed to take place very rapidly in air, the temperature of the surrounding air will;
Decrease
One Joule is equivalent to:
1/4.184 cal
The heat of reaction depends upon:
➡Temperature of the Reaction
➡Physical states of the reactants and the products
The exothermic process is;
Respiration
During an exothermic or endothermic reaction, one of the following formulas is used to calculate the amount of heat evolved or absorbed:
q = m x s x ΔT
Most of the reactions which give stable products are;
Exothermic
The measurement of enthalpy change at standard conditions means that we should manage the measurement at:
25°C at 1 atm
The total heat content of a system is called:
Enthalpy
