Answers posted by mosymeow_1

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The amount of heat evloved when 500 $cm^3$ 0.1 M HCl is mixed with 200 $cm^3$ of 0.2 M NaOH is

answered Feb 27, 2014

Answer: 2.292 kJ500 $cm^3$ of 0.1 M HCl = $\frac{500 \times 0.1}{1000}$ = 0.05 mol200 $cm^3$ of 0.2 ...

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$H_2O(g) + C(s) \rightarrow CO(g) + H_2(g)$ ; $\Delta H = 131$ kJ. $CO(g) + \frac{1}{2} O_2(g) \rightarrow CO_2(g)$ ; $\Delta H = -282$ kJ. $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(g)$ ; $\Delta H = -242$ kJ. $C(s) + O_2(g) \rightarrow CO_2(g)$ ; $\Delta H = X $ kJ. Based on the above thermochemical equations find the value of X.

answered Feb 27, 2014

Answer: -393 kJ$H_2O(g) + C(s) \rightarrow CO(g) + H_2(g)$ ; $\Delta H = 131$ kJ. $CO(g) + \frac{1}{...

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10 moles of an ideal gas expands into vacuum. The work done is

answered Feb 27, 2014

Answer: zeroIf an ideal gas expand against vacuum, the irreversible expansion is called free expansi...

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The source of energy in a cellular reaction is

answered Feb 27, 2014

Answer: chemical energyCellular reaction mainly refers to metabolism which is essentially bond makin...

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The heat liberated when $1.89\; g$ of benzoic acid is burnt in a bomb calorimeter at $25^\circ C$ increases the temperature of $18.94\; kg$ of water by $0.632^\circ C$. If the specific heat of water at $25^\circ C$ is $0.998 \;cal/g$ deg, the value of the heat of combustion of benzoic acid is

answered Feb 27, 2014

Answer: 771.4 kcalGiven, Weight of benzoic acid = 1.89 gTemperature of bomb calorimeter = $25^\circ ...

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What is the P-P bond energy in kJ/mol, if the heat of atomisation of $PH_3(g)$ and $P_2H_4(g)$ are 954 kJ/mol and 1485 kJ/mol, respectively?

answered Feb 27, 2014

Answer: 213Atomisation energy of $PH_3 = 3\times BE(P-H) = 954$ kJ/mol$\therefore BE(P-H) = \frac{95...

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Let the activation energies of two reactions be $E_1$ and $E_2$ where $E_1>E_2$. If temperature of the system is increased from $T_1$ to $T_2$, the rate constant of the reactions changes from $k_1$ to $k_1'$ in the first reaction and from $k_2$ to $k_2'$ in the second reaction. Which of the following expression is correct?

answered Feb 27, 2014

Answer: $\frac{k_1'}{k_1} > \frac{k_2'}{k_2}$We know, log $\frac{k_2}{k_1} = \frac{E_a}{2.303 R}[...

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Which one of the following equation is true? (Given, $\delta E = T\delta S -P\delta V$ and $H=E+PV$)

answered Feb 27, 2014

Answer: $\delta H = T\delta S + V\delta P$Given, $H = E + PV$Differentiating both sides we get,$\del...

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The reaction $A \leftrightharpoons B$; $\Delta H = +24\; kJ/mol$. For the reaction $B\leftrightharpoons C$; $\Delta H=-18$ kJ/mol. The decreasing order of enthalpy of $A, B$ and $C$ follow the order

answered Feb 27, 2014

Answer: B, C, ALet $\Delta H_f (A) = x$ kJ/mol$A\longrightarrow B$ ; $\Delta H$ = + 24 kJ/mol$\Delta...

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The enthalpy of neutralisation of oxalic acid by strong base is 25.4 kcal/mol. The enthalpy of neutralisation of strong acid and strong base is -13.7 kcal/equil. The enthalpy of dissociation of $H_2C_2O_4 \leftrightharpoons 2H^+ + C_2O_4^{2-}$ is

answered Feb 27, 2014

Answer: 2.0 kcal/molEnthalpy of dissociation of oxalic acid = Heat of neutralisation of a strong aci...

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Cooking is fast in a pressure cooker because

answered Feb 27, 2014

Toolbox:Pressure cookers heat food quickly because the internal steam pressure from the boiling liqu...

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To raise the temperature of 4.48 litres of an ideal gas at STP by $15^\circ C$ it requires 12.0 calories. The $C_P$ of the gas is

answered Feb 27, 2014

Answer: 6 calNo. of moles in 4.484 of ideal gas at STP = $\frac{4.48}{22.4} = 0.2$Thus to raise the ...

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How many calories are required to heat 40 grams of argon from $40-100^\circ C$ at constant volume? (R = 2 cal/mol K)

answered Feb 27, 2014

Answer: 180For a monoatomic gas like argon, $C_V$ = 3 cal/mol, $C_P$ = 5 cal/mol.Molar heat capacity...

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$\Delta G^\circ$ for a reaction is 46.06 kcal/mol, $K_P$ for the reaction at 300 K is

answered Feb 27, 2014

Answer: $10^{-33.55}$$\Delta G^\circ$ = 46.06 kcal/mol = $46.06 \times 1000 \times 4.184 J/mol$$\Del...

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Enthalpy =

answered Feb 27, 2014

Answer: $-T^2 [\frac{\delta(G/T)}{\delta T}]_P$It can be derived from the definition of Entropy and ...

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Given, the enthalpy of combustion of glucose is 3000 kJ/mol. How much of glucose one has to consume to walk a distance of 5 km, provided 150 kJ of energy is needed for muscular work to walk a distance of 1 km and only 30 % energy is available for muscular work?

answered Feb 27, 2014

Answer: 150 gEnergy consumed for walking a distance of 5 km = 150 $\times$ 5 kJ = 750 kJ1 mole of gl...

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When 0.1 mole of a gas absorbs 41.75 J of heat, the rise in temperature occurs equal to $20 ^\circ C$. The gas must be

answered Feb 27, 2014

Toolbox:$C_P = C_V + R $Answer: monoatomic$C_V$ (heat absorbed per degree rise per mole) = $\frac{41...

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Enthalpy of formation of (C=C) and (C-C) in $C_2H_4$ is -590 kJ/mol and -331 kJ/mol, respectively. What is the enthalpy change when ethylene polymerises to form polythene?

answered Feb 27, 2014

Answer: -72 kJ/mol In the given polymerisation reaction, one mole of ethylene involves breaking of o...

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At 273 K the enthalpy of a certain reaction is -20.75 kJ. If heat capacities of the reactants and products are the same, then what will be the enthalpy of the same reaction at 373 K?

answered Feb 27, 2014

Answer: -20.75 kJBy Kirchoff's equation $\frac{\Delta H_2 - \Delta H_1}{T_2 - T_1} = \Delta C_P$Sinc...

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$CO(g) + \frac{1}{2} O _2 \longrightarrow CO_2$, $\Delta H$ and $\Delta S$ for the reaction are $-283\; KJ$ and $-87\; JK^{-1}$. It was intended to carry out this reaction at $1000, 1500, 3000$ and $3500\; K$. At which of these temperatures would this reaction be thermodynamically spontaneous?

answered Feb 27, 2014

Answer: 1000, 1500 and 3000 KFor the reaction to be spontaneous : $\Delta G < 0$$\Delta G = \Delt...

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Some equations are given below. Which of the following processes does not correctly represent the first law of thermodynamics ?

answered Feb 27, 2014

Toolbox:The 1st Law of Thermodyamics simply states that energy can be neither created nor destroyed ...

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To 100 $cm^3$ water at 298 K, 0.06 mole of $KNO_3$ is added. The enthalpy of $KNO_3$(aq) solution is 35.8 kJ $mol^{-1}$. What will be the temperature of the solution, after the solute is dissolved?

answered Feb 27, 2014

Answer: 293 KDissolution of $KNO_3$ is endothermic.$\Delta H_{sol}$ = 35.8 kJ $mol^{-1}$$\therefore ...

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Study the given diagram. 3 moles of gas is put through a series of thermodynamic changes as shown graphically in a cyclic process. The processes A $\rightarrow$ B, B $\rightarrow$ C and C $\rightarrow$ A respectively are

answered Feb 27, 2014

Answer: isochoric, isobaric, isothermalAs shown in the figure,Process A $\rightarrow$ B is isochoric...

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Heat of neutralisation of HCl with $NH_4OH$ and NaOH with $CH_3COOH$ are respectively -51.4 and -50.6 kJ $eq^{-1}$. What will be the heat of neutralisation of acetic acid with $NH_4OH$?

answered Feb 26, 2014

Answer: -44.6 kJ $eq^{-1}$(i) $HCl + NH_4OH \longrightarrow NH_4Cl + H_2O$ ; $\Delta H = -51.4 kJ$(...

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If the heat of neutralisation for a strong acid-base reaction is -57.1 kJ what would be the heat released when 350 $cm^3$ of 0.20 M $H_2SO_4$ is mixed with 650 $cm^3$ of $0.10\; M\; NaOH$ ?

answered Feb 26, 2014

Answer: 3.71 kJ Amount of $H^+$ ions = M $\times$ V = 0.20 $\times$ 350 =70 m mol$\therefore$ A...

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If the bond dissociation energies of the diatomic molecules $XY, X_2$ and $Y_2$ are in the ratio of 1 : 1 : 0.5 and $\Delta_fH$ for the formation of XY is -200 kJ $mol^{-1}$. What is the bond dissociation energy of $X_2$ will be

answered Feb 26, 2014

Answer: 800 kJ $mol^{-1}$$X-X + Y-Y \rightarrow 2 X-Y$ ; $\Delta H = -200 \times 2 $ kJLet, B.E. of ...

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$N_2 + 3H_2 \longrightarrow 2NH_3$ This reaction is carried out at constant temperature and pressure. If $\Delta H$ and $\Delta U$ are enthalpy and internal energy change for the reaction, which of the following expression is true?

answered Feb 26, 2014

Answer: $\Delta H < \Delta U$$N_2 + 3H_2 \longrightarrow 2NH_3$$\Delta n_g$ = 2 - 4 = -2Now, $\De...

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For a spontaneous reaction, the $\Delta G$, equilibrium constant, K and $E^\circ _{cell}$ will be respectively

answered Feb 26, 2014

Toolbox:∆ G= free energy, spontaneity Negative: spontaneous Positive: non-spontaneous Equal to Zero:

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$MgO(s) + 2HCl(aq) \longrightarrow MgCl_2(aq) + H_2O(l)$; The absolute enthalpy of neutralisation of the reaction is

answered Feb 26, 2014

Answer: greater than -57.33 kJ $mol^{-1}$The absolute value of enthalpy of neutralisation of this r...

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How much heat would release when an aqueous solution containing 0.5 mol of $HNO_3$ is mixed with 0.3 mol of $OH^{-1}$? Given, enthalpy of neutralisation is -57.1 kJ.

answered Feb 26, 2014

Answer: 17.1 kJ0.5 mol $HNO_3 \equiv$ 0.5 mol $H^+$$H^+ + OH^- \longrightarrow H_2O$ ; $\Delta H = -...

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At 1 atm pressure, for a reaction $\Delta H = + 30.558$ kJ $mol^{-1}$ and $\Delta S = 0.066$ kJ $mol^{-1}$. The temperature at which free energy is equal to zero and the nature of the reaction below this temperature are

answered Feb 26, 2014

Answer: 463 K, non-spontaneous$\Delta G = \Delta H - T \Delta S = 0$$\therefore T = \frac{\Delta H}{...

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Study the following table and, on the basis of these values of $\Delta H$ and $\Delta S$ for five different reactions, predict which one of these will be spontaneous at all temperatures?

answered Feb 26, 2014

Toolbox:Answer: Reaction IVFor, reaction to be spontaneous at all temperatures $\Delta S$ should be ...

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A cylinder of gas is assumed to contain 14 kg of butane. A normal family requires 20,000 kJ of energy per day for cooking. How many days will the butane gas in the cylinder last?

answered Feb 26, 2014

Answer: 32 daysMolar mass of butane, $C_4H_{10} = 12 \times 4 + 10 = 58 g mol^{-1}$58 g of butane gi...

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What is the change in entropy of 1 mole of a perfect gas, which expands isothermally to ten times its original volume?

answered Feb 26, 2014

Toolbox:$W_{rev} = -$2.303 nRT $log \frac{V_2}{V_1}$Change in Entropy $\Delta S = \frac{q_{rev}}{T}$...

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The heat liberated when 50 $cm^3$ of 0.2 N $H_2SO_4$ is mixed with 50 $cm^3$ of 1 N KOH, is

answered Feb 25, 2014

Answer: 573 JHere, $H_2SO_4$ is the limiting reactant. Since, $N_1V_1 = N_2V_2$$0.2 \times 50 = 1 \t...

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Show the relation between the enthalpies of the reactions: $H_2(g)+ \frac{1}{2} O_2(g) \rightarrow H_2O(g); \Delta H_1$ and $H_2(g)+\frac{1}{2}O_2(g) \rightarrow H_2O(l); \Delta H_2$

answered Feb 25, 2014

Answer: $\Delta H_1 < \Delta H_2 $Given these two equations,$H_2(g)+ \frac{1}{2} O_2(g) \rightarr...

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What is the standard Gibbs energy change for the reaction at 298 K, if standard enthalpy and standard entropy changes for the oxidation of ammonia at 298 K are 382.64 kJ $mol^{-1}$ and -145.6 $JK^{-1}mol^{-1}$, respectively.

answered Feb 25, 2014

Answer: -339.3 kJ $mol^{-1}$$NH_3 (g) + \frac{3}{2}O_2(g) \rightarrow \frac{1}{2}N_2(g) + \frac{3}{2...

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How much heat is liberated when 100 mL of 1 N NaOH is neutralised by 300 mL of 1 N HCl ?

answered Feb 25, 2014

Answer: 5.73 kJ100 mL of 1 N NaOH will be exactly neutralised with 100 mL of 1 N HCl.1000 mL of 1 N ...

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Keeping in mind the enthalpy of formation of HF and HCl i.e. -161 kJ and -92 kJ, respectively, which of the following statements do you think is incorrect?

answered Feb 25, 2014

Toolbox:Compounds for which $\Delta H_f$ is negative is more stable than the compound for which $\De...

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The molar heat capacity of water at constant pressure, $C_P$ is $75JK^{-1}mol^{-1}$. When 1.0 kJ of heat is supplied to 100 g of water which is free to expand, the increase in temperature of water is

answered Feb 25, 2014

Answer: 2.4 K Given, Heat supplied to 100 gm of water, Q = 1 kJ = 1000Jmass of water, m =100 g ...

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Heat of combustion $\Delta H$ for $C(s), H_2(g)$ and $CH_4(g)$ are -94, -68 and -213 kcal/mol. Then $\Delta H$ for $C(s) + H_2(g) \rightarrow CH_4(g)$ is

answered Feb 25, 2014

Answer: -17 kcal (i) $C(s) + 2H_2(g) \rightarrow CH_4(g)$(ii) $C(s) + O_2(g) \rightarrow CO_2(g...

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Which of the following condition depicts a favourable condition for a spontaneous reaction?

answered Feb 25, 2014

Toolbox:$\Delta G = \Delta H - T\Delta S$For a process to be spontaneous, $\Delta G$ should be negat...

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Assume the enthalpy of combustion of methane and $CH_3OH$ are $x$ and $y$ respectively. If the enthalpy of $CH_4 + \frac{1}{2}O_2 \rightarrow CH_3OH$ is negative, then which relation is correct?

answered Feb 25, 2014

Answer: $x > y$ On combustion of methane,$CH_4 + O_2\rightarrow CO_2 + 2H_2O$ ; $\Delta H_1 ...

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Given three reaction below, $N_2(g) + 3H_2(g) \leftrightharpoons 2NH_3(g); \Delta H_1$, $H_1(g) + Cl_2(g) \leftrightharpoons 2HCl(g) ; \Delta H_2$, $NH_3 (g) + 3Cl_2 \leftrightharpoons NCl_3(g) + 3HCl(g); -\Delta H_3$. In the terms of $\Delta H_1, \Delta H_2$ and $\Delta H_3$, heat of formation of $NCl_3(g)$ is

answered Feb 25, 2014

Answer: $\Delta H_f = -\Delta H_3 + \frac{\Delta H_1}{2} - \frac{3}{2} \Delta H_2$ The reaction...

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The following table lists the bond dissociation energy ($E_{diss}$) for single covalent bonds formed between C and atoms A, B, D, E. Which of the atoms has smallest size?

answered Feb 25, 2014

Toolbox:Smaller the atom, more effective will be the orbital overlap and larger will be bond dissoci...

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What is the work done when 1 mol of water at 373 K vapourises against atmospheric pressure of 1.0 atmosphere? [Solve the question assuming ideal gas behaviour]

answered Feb 25, 2014

Answer: -3100 J Volume of 1 mol of water at 373 K, 1 atm ($V_1$) = $18 cm^3$ = 0.018 LVolume of...

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My name was suggested by Davy on account of my colour i.e. greenish yellow. I have a pungent and suffocating odour. I am about 2.5 times heavier than air. I am soluble in water and also have a great affinity for hydrogen. WHO AM I?

answered Feb 25, 2014

Answer: Chlorine Chlorine was discovered in 1774 by Scheele by the action of HCl on $MnO_2$. In...

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I am a pale blue gas, dark blue liquid and violet-black solid. I am thermodynamically unstable with respect to oxygen. I am a powerful oxidising agent. If my concentration in air rises, your breathing becomes uncomfortable resulting in headache and nausea. WHO AM I?

answered Feb 25, 2014

Answer: Ozone Pure ozone is a pale blue gas, dark blue liquid and violet-black solid. Ozone has...

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Given $\Delta H^\circ _{ioniz}$ (HCN) = 45.2 kJ $mol^{-1}$ and $\Delta H^\circ _{ioniz} (CH_3COOH)$ = 2.1 kJ $mol^{-1}$. Which one of the following fact is true?

answered Feb 24, 2014

Toolbox:Smaller the $pK_a$ value, stronger the acid.Answer: $pK_a (HCN) > pK_a (CH_3COOH)$HCN has...

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The heat evolved in combustion of benzene is given by the following equation: $C_6H_6 + \frac{15}{2} \rightarrow 3H_2O + 6CO_2$; $\Delta H= - 3264.6 kJ$ Which of the following quantities of heat will be evolved when 39 g of benzene are burnt in an open container?

answered Feb 24, 2014

Answer : -1632.3 kJ$C_6H_6 + \frac{15}{2} \rightarrow 3H_2O + 6CO_2$; $\Delta H= - 3264.6 kJ$78 gm o...

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