The standard molar entropy of H2O (l )
Question: The standard molar entropy of H2O (l ) is 70 J K1 mol1. Will the standard molar entropy of H2O(s) be more, or less than 70 J K1 mol1? Solution: The entropy of H2O(s) entropy of H2O (l ). The standard molar entropy of H2O(s) will also be less than 70 J K1 mol1....
Read More →As thermal equilibrium obeys the zeroth
Question: As thermal equilibrium obeys the zeroth law of thermodynamics, temperature of system and surroundings will be the same when they are in thermal equilibrium. Solution: For the given reaction N2O4 (g) ⇋2NO2 (g) the value of Kp = 0.98. Hence, ∆rG⁰ = RT ln(0.98) Since ln(0.98) has a negative value, the value of ∆rG⁰ becomes positive. Therefore, the reaction is non- spontaneous....
Read More →Find the coordinates of the point which divides the join of A
Question: Find the coordinates of the point which divides the join of A(-5, 11) and B(4, -7) in the ratio 2 : 7. Solution: Let P(x, y) be the point that divides the join of A(-5, 11) and B(4, -7) in the ratio 2 : 7 Formula: If $m_{1}: m_{2}$ is the ratio in which the join of two points is divided by another point $(x, y)$, then $\mathrm{x}=\frac{\mathrm{m}_{1} \mathrm{x}_{2}+\mathrm{m}_{2} \mathrm{x}_{1}}{\mathrm{~m}_{1}+\mathrm{m}_{2}}$ $\mathrm{y}=\frac{\mathrm{m}_{1} \mathrm{y}_{2}+\mathrm{m}...
Read More →Increase in enthalpy of the surroundings
Question: Increase in enthalpy of the surroundings is equal to the decrease in enthalpy of the system. Will the temperature of the system and surroundings be the same when they are in thermal equilibrium? Solution: As thermal equilibrium obeys the zeroth law of thermodynamics, temperature of system and surroundings will be the same when they are in thermal equilibrium....
Read More →Show that the following curves intersect orthogonally at the indicated points :
Question: Show that the following curves intersect orthogonally at the indicated points : $y^{2}=8 x$ and $2 x^{2}+y^{2}=10$ at $(1,2 \sqrt{2})$ Solution: Given: Curves $y^{2}=8 x \ldots(1)$ $\ 2 x^{2}+y^{2}=10 \ldots(2)$ The point of intersection of two curves are $(0,0) \(1,2 \sqrt{2})$ Now, Differentiating curves (1) \ (2) w.r.t x, we get $\Rightarrow y^{2}=8 x$ $\Rightarrow 2 y \cdot \frac{d y}{d x}=8$ $\Rightarrow \frac{d y}{d x}=\frac{8}{2 y}$ $\Rightarrow \frac{d y}{d x}=\frac{4}{y} \ldot...
Read More →The heat has a randomising influence on a system
Question: The heat has a randomising influence on a system and temperature is the measure of average chaotic motion of particles in the system. Write the mathematical relation which relates these three parameters. Solution: The mathematical relation which relates these three parameters is ΔS = qrev/T where ΔS is the change in entropy and T stands for temperature....
Read More →Given that ΔH = 0 for mixing of two gases.
Question: Given that ΔH = 0 for mixing of two gases. Explain whether the diffusion of these gases into each other in a closed container is a spontaneous process or not? Solution: A negative ∆G means the reaction will be the spontaneous included contribution of the other factors like enthalpy(H) and entropy(S). ∆G= ∆H T∆S ∆H being 0, ∆G will be negative (as the positive value of ∆S will give a more negative T∆S) ∆H=0 ; ∆G= -T∆S= negative....
Read More →Find the area of ΔABC, the midpoints of whose sides AB,
Question: Find the area of ΔABC, the midpoints of whose sides AB, BC and CA are D(3, -1), E(5, 3) and F(1, -3) respectively. Solution: The figure is as shown above. $x_{1}+x_{2}=2 \times 3=6 \ldots .(1)$ $x_{1}+x_{3}=2 \times 1=2 \ldots \ldots(2)$ $x_{2}+x_{3}=2 \times 5=10 \ldots \ldots(3)$ Equation 1 - Equation 2 gives us $\mathrm{X}_{2}-\mathrm{X}_{3}=4$ ..........(4) Equation 3 + Equation 4, $2 x_{2}=14 \Rightarrow x_{2}=7$ $\therefore \mathrm{x}_{1}=-1$ and $\mathrm{x}_{3}=3$ Similarly, $y_...
Read More →Use the following data to calculate Δlattice HΘfor NaBr.
Question: Use the following data to calculate Δlattice HΘfor NaBr. Δsub HΘfor sodium metal = 108.4 kJ mol1 Ionization enthalpy of sodium = 496 kJ mol1 Electron gain enthalpy of bromine = 325 kJ mol1 Bond dissociation enthalpy of bromine = 192 kJ mol1 Δf HΘfor NaBr (s) = 360.1 kJ mol1 Solution: Sublimation of the metal(ΔsubHΘ) Ionization of the metal (ΔiHΘ) Dissociation of the non-metal (ΔdissHΘ) Gain of electrons by the non-metal(ΔegHΘ) Δf HΘ =Δsub HΘ+Δi HΘ+1/2 dissHΘ + ΔegHΘ+ ΔlattticeHΘ To cal...
Read More →Show that the following curves intersect orthogonally at the indicated points :
Question: Show that the following curves intersect orthogonally at the indicated points : $x^{2}=y$ and $x^{3}+6 y=7$ at $(1,1)$ Solution: Given: Curves $x^{2}=y \ldots$ (1) $\ x^{3}+6 y=7 \ldots(2)$ The point of intersection of two curves $(1,1)$ Solving (1) \ (2), we get, First curve is $x^{2}=y$ Differentiating above w.r.t $x$, $\Rightarrow 2 x=\frac{d y}{d x}$ $\Rightarrow \frac{d y}{d x}=2 x$ .....(3) Second curve is $x^{3}+6 y=7$ Differentiating above w.r.t $x$, $\Rightarrow 3 x^{2}+6 \cdo...
Read More →The enthalpy of atomisation for the reaction
Question: The enthalpy of atomisation for the reaction CH4(g) C(g) + 4H (g) is 1665 kJ mol1. What is the bond energy of the CH bond? Solution: For 1 C-H bond, the bond energy will be equal to 1/4 that of the enthalpy of atomisation = (1665/4) = 416.25 kJ mol1....
Read More →Enthalpy is an extensive property.
Question: Enthalpy is an extensive property. In general, if the enthalpy of an overall reaction AB along one route is Δr H and Δr H1, ΔrH2, ΔrH3 .. represent enthalpies of intermediate reactions leading to product B. What will be the relation between ΔrH for overall reaction and ΔrH1, ΔrH2.. etc. for intermediate reactions. Solution: For the reaction, AB the formation of B goes through several intermediate reactions with different enthalpy values Δr H1, ΔrH2, ΔrH3.., and the overall enthalpy cha...
Read More →The value of ΔfHΘfor NH3 is – 91.8 kJ mol–1.
Question: The value of ΔfHΘfor NH3 is 91.8 kJ mol1. Calculate the enthalpy change for the following reaction : 2NH3(g) N2(g) + 3H2(g) Solution: Enthalpy change of a reaction is calculated as : Σbond enthalpy of reactants- Σbond enthalpy of products for the decomposition 2NH3(g) N2(g) + 3H2(g) ΔrHΘ will be = ( 91.8 kJ mol1 ) = + 91.8 kJ mol1 for 2 moles of NH3 enthalpy change of the reaction will be ΔrH = (2 X 91.8 ) = 183.6 kJ mol1 ....
Read More →Standard molar enthalpy of formation,
Question: Standard molar enthalpy of formation, Δf HΘis just a special case of enthalpy of reaction, Δr HΘ. Is the Δr HΘfor the following reaction same as Δf HΘ? Give the reason for your answer. CaO(s) + CO2(g) CaCO3(s) ; ΔfHΘ = 178.3 kJ mol1 Solution: The given reaction CaO(s) + CO2(g) CaCO3(s) is indicating that it is occurring in the standard form of 1 mole of each substance. And the molar enthalpy of formation ΔfHΘ = 178.3 kJ mol1 Given for CaCO3 is also showing the standard conditions. So,Δ...
Read More →One mole of acetone requires less heat
Question: One mole of acetone requires less heat to vaporise than 1 mol of water. Which of the two liquids has a higher enthalpy of vapourisation? Solution: Among the two liquids, water has a higher enthalpy of vapourisation (consuming higher heat energy). Therefore, ∆Hvapourisation (water) ∆Hvapourisation (acetone)....
Read More →18.0 g of water completely vapourises at
Question: 18.0 g of water completely vapourises at 100C and 1 bar pressure and the enthalpy change in the process is 40.79 kJ mol1. What will be the enthalpy change for vapourising two moles of water under the same conditions? What is the standard enthalpy of vapourisation for water? Solution: Enthalpy change of vapourisation for 1 mole = 40.79 kJ mol1 enthalpy change of vapourisation for 2 moles of water = (40.79 2) = 81.58kJ mol1 for water ∆Hvapourisation, ⁰ will be equal to =40.79 kJ mol1...
Read More →Consider the following reaction between zinc and oxygen
Question: Consider the following reaction between zinc and oxygen and choose the correct options out of the options given below : 2 Zn (s) + O2 (g) 2 ZnO (s) ; ∆H = 693.8 kJ mol1 (i) The enthalpy of two moles of ZnO is less than the total enthalpy of two moles of Zn and one mole of oxygen by 693.8 kJ. (ii) The enthalpy of two moles of ZnO is more than the total enthalpy of two moles of Zn and one mole of oxygen by 693.8 kJ. (iii) 693.8 kJ mol1 energy is evolved in the reaction. (iv) 693.8 kJ m...
Read More →Find the area of the quadrilateral whose vertices are
Question: Find the area of the quadrilateral whose vertices are A(-4, 5), B(0, 7), C(5, -5) and D(-4, -2). Solution: Given: The vertices of the quadrilateral are A(-4, 5), B(0, 7), C(5, -5) and D(-4, -2). Formula: Area of a triangle $=\frac{1}{2}\left[\mathrm{x}_{1}\left(\mathrm{y}_{2}-\mathrm{y}_{3}\right)+\mathrm{x}_{2}\left(\mathrm{y}_{3}-\mathrm{y}_{1}\right)+\mathrm{x}_{3}\left(\mathrm{y}_{1}-\mathrm{y}_{2}\right)\right]$ Area of quadrilateral ABCD = Area of Δ ABC + Area of Δ ADC $=\frac{1}...
Read More →For an ideal gas,
Question: For an ideal gas, the work of reversible expansion under isothermal condition can be calculated by using the expression w = nRT ln Vf/Vi A sample containing 1.0 mol of an ideal gas is expanded isothermally and reversibly to ten times of its original volume, in two separate experiments. The expansion is carried out at 300 K and 600 K respectively. Choose the correct option. (i) Work done at 600 K is 20 times the work done at 300 K. (ii) Work done at 300 K is twice the work done at 600 K...
Read More →The spontaneity means,
Question: The spontaneity means, having the potential to proceed without the assistance of an external agency. The processes which occur spontaneously are (i) flow of heat from colder to warmer body. (ii) gas in a container contracting into one corner. (iii) gas expanding to fill the available volume. (iv) burning carbon in oxygen to give carbon dioxide. Solution: Option (iii) gas expanding to fill the available volume and (iv)burning carbon in oxygen to give carbon dioxide are the answers....
Read More →In an exothermic reaction,
Question: In an exothermic reaction, heat is evolved, and the system loses heat to the surrounding. For such a system (i) qp will be negative (ii) ∆rH will be negative (iii) qp will be positive (iv) ∆rH will be positive Solution: Option (i)qp will be negative and (ii)∆rH will be negative are the answers....
Read More →Thermodynamics mainly deals with
Question: Thermodynamics mainly deals with (i) interrelation of various forms of energy and their transformation from one form to another. (ii) energy changes in the processes which depend only on initial and final states of the microscopic systems containing a few molecules. (iii) how and at what rate these energy transformations are carried out. (iv) the system in equilibrium state or moving from one equilibrium state to another equilibrium state. Solution: Option (i)interrelation of various f...
Read More →Which of the following is not
Question: Which of the following is not correct? (i) ∆G is zero for a reversible reaction (ii) ∆G is positive for a spontaneous reaction (iii) ∆G is negative for a spontaneous reaction (iv) ∆G is positive for a non-spontaneous reaction Solution: Option (ii) ∆G is positive for a spontaneous reactionis the answer....
Read More →Enthalpy of sublimation of a substance
Question: Enthalpy of sublimation of a substance is equal to (i) enthalpy of fusion + enthalpy of vapourisation (ii) enthalpy of fusion (iii) enthalpy of vapourisation (iv) twice the enthalpy of vapourisation Solution: Option (i)enthalpy of fusion + enthalpy of vapourisation is the answer....
Read More →The enthalpies of elements
Question: The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound (i) is always negative (ii) is always positive (iii) maybe positive or negative (iv) is never negative Solution: Option (iii) maybe positive or negativeis the answer....
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