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Answers posted by mosymeow_1
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The heat change for the following reaction at 298 K and constant pressure is +7.3 kcal. $A_2B(s) \rightarrow 2A(s) + \frac{1}{2} B_2(g)$; $\Delta H = + 7.3 kcal$ The heat change at constant volume would be
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Feb 24, 2014
Answer: Less than +7.3 kcal$\Delta H = \Delta E + \Delta n_g RT$or $\Delta E = \Delta H - \Delta n_g...
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The enthalpy change at 298 K of the reaction $H_2O_2(l) \longrightarrow H_2O (l) + \frac{1}{2} O_2 (g)$ is -23.5 kcal $mol^{-1}$ and enthalpy of formation of $H_2O_2(l)$ is -44.8 kcal $mol^{-1}$. The enthalpy of formation of $H_2O(l)$ is
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Feb 24, 2014
Answer: kcal $mol^{-1}$Given(i) $H_2O_2(l) \longrightarrow H_2O (l) + \frac{1}{2} O_2 (g)$; $\Delta...
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The work done on the system when one mole of an ideal gas at 500 K is compressed isothermally and reversibly to 1/10th of its original volume (R = 2 cal)
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Feb 24, 2014
Toolbox:Work done on the system W= - 2.303 nRT log$\frac{V_2}{V_1}$Answer: 2.303 kcalSince, work don...
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An ideal gas expands from $10^{-3} m^3$ to $10^{-2} m^3$ at 300 K, against a constant pressure of $10^5 N m^{-2}$. The work done on it is
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Feb 24, 2014
Answer: -0.9 kJ$W = - P \Delta V$$P = 10^5 Nm^{-2}$ = 1 atm$\Delta V$ = 10 -1 = 9 Litres [$1m^3 = 10...
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For the reaction between $CO_2$ and graphite $CO_2(g) + C(s) \longrightarrow 2CO(g)$ $\Delta H = +170.0 kJ$ and $\Delta S = 170 JK^{-1}$. The reaction is spontaneous at
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Feb 24, 2014
Answer: 1200 K$\Delta H$ = 170,000 J and $\Delta S = 170 JK^{-1}$When, $\Delta G = 0$ (equilibrium)A...
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An engine operating between $100^\circ C$ and $0^\circ C$ takes 453.6 Kcal of heat. How much useful work can be done by it?
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Feb 24, 2014
Answer: 508.8 kJ$T_2$ = 100 + 273 = 373 K and$T_1$ = 0 + 273 = 273 KQ = 453.6 kcal = 453.6 $\times$...
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What percent $T_1$ is of $T_2$ for a heat engine whose efficiency is 10%?
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Feb 24, 2014
Toolbox:Efficiency of a heat engine, $\eta = 1 - \frac{T_1}{T_2}$ Answer: 90%Since, efficiency of a ...
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The heat change at constant volume for the decomposition of silver(I) oxide is found to be 30.66 kJ. The heat change at constant pressure will be
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Feb 24, 2014
Answer: > 30.66 kJHeat change at constant volume for the decomposition of silver(I) oxide = 30.6...
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At 298 K, the enthalpy change for a given reaction K is $-x$ cal/mol. If the reaction occurs spontaneously at 298 K, the entropy change at that temperature
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Feb 24, 2014
Toolbox:$\Delta G = \Delta H - T\Delta S$Answer: can be negative, but numerically smaller than $\fr...
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For the following thermodynamic process Dry ice $\longrightarrow CO_2$ (g)
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Feb 24, 2014
Answer: Both $\Delta H$ and $\Delta S$ are positiveDry ice $\Rightarrow CO_2$.This reaction is known...
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The sign of $\Delta G$ for the process of melting of ice at 273 K and 1 atm pressure is
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Feb 24, 2014
Toolbox:Melting of ice is spontaneous above 273 K at one atm pressure. Answer: neither negative nor ...
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According to third law of thermodynamics, the entropy at 0 K is zero for
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Feb 24, 2014
Answer: perfectly crystalline solidsThe Third Law of Thermodynamics states, “The entropy of a perfec
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The value of $\Delta S$ is negative in which of the following process?
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Feb 24, 2014
Answer: Stretching of rubber bandIn rubber the long flexible macromolecules coil up in a random way....
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For the gaseous reaction involving the complete combustion of isobutane
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Feb 24, 2014
Toolbox:When, $\Delta n_g = +ve, \Delta H > \Delta E$When, $\Delta n_g = -ve, \Delta H < \Delt...
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Enthalpy of neutralisation of all strong acids and strong bases has the same value because
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Feb 23, 2014
Answer: the net chemical change involve the combination of 1 mol of $H^+$ ions and ions $OH^-$ ions ...
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One gram of diamond atom of graphite and one gram atom of diamond were separately burnt to carbon dioxide. The amount of heat liberated were 393.5 kJ and 395.4 kJ respectively. It follows that
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Feb 23, 2014
Answer: graphite is more stable than diamondSince graphite on combustion gives less heat, it means g...
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X gm of ethanal was subjected to combustion in a bomb calorimeter. The heat produced is Y joules. Then
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Feb 23, 2014
Answer: $\Delta E_{(combustion)} = - \frac{44Y}{X} J mol^{-1}$$CH_3CHO + \frac{5}{2} O_2 + \longrigh...
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The reaction $SO_2(g) + \frac{1}{2} O_2 (g) \longrightarrow SO_3(g)$ should be
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Feb 23, 2014
Answer: ExothermicThe reaction involves decrease in randomness, therefore its spontaneity must be fa...
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Which of the following relationship is not correct?
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Feb 23, 2014
Answer: $\Delta H$ is less than $\Delta E$ for combustion of carbon to carbonIn the formation of $C...
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At constant volume the heat of combustion of solid benzoic acid is -321.30 kJ at $27^\circ C$. The heat of combustion at constant pressure is
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Feb 23, 2014
Answer: -321.30 - 150 R$C_6H_5COOH (s) + \frac{15}{2} O_2(g) \longrightarrow 7CO_2(g) + 3H_2O(l)$Sin...
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What is observed during isothermal expansion of an ideal gas?
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Feb 23, 2014
Toolbox:During Isothermal expansion of an ideal gas $\Delta E=0, \Delta T=0$Answer: Enthalpy remains...
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When is the efficiency of a heat engine maximum?
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Feb 23, 2014
Toolbox:Efficiency of a heat engine, $\eta = \frac{T_2 - T_1}{T_2}$Answer: temperature difference of...
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Identify the correct order of solubility of $Na_2S, CuS$ and $ZnS$ in aqueous solution
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Feb 1, 2014
Toolbox:More the $K_{sp}$, for similar compounds more is the solubility. Answer: $Na_2S > ZnS >...
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The reagent $NH_4Cl$ and aqueous $NH_3$ will precipitate
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Feb 1, 2014
Answer: $Al^{3+}$ Group reagent for group III ($NH_4Cl$ and $NH_4OH$) can precipitate group I,...
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Potassium ferrocyanide is used in the detection of
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Feb 1, 2014
Answer: $Fe^{3+}$ ions $4FeCl_3 + 3K_4[Fe(CN)_6] \longrightarrow Fe_4[Fe(CN)_6]_3 $ (Prussian...
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A red solid is insoluble in water. However, it becomes soluble if some KI is added to water. Heating red solid in a test tube produces violet coloured fumes and droplets of metal appear on the cooler parts of test tube. The red solid is
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Feb 1, 2014
Answer: $HgI_2$ $HgI_2$ is a scarlet red compound which is insoluble in water$HgI_2 + 2KI \long...
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Which of the following metal sulphides has maximum solubility in water?
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Feb 1, 2014
Answer: FeS $K_{sp} = 10^{-20}$ More the $K_{sp}$ more is the solubility as all sulphides are ...
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When chlorine water is added to an aqueous solution of potassium halide in the presence of chloroform, a violet colour is obtained. On adding more of chlorine water, the violet colour disappears, and a colourless solution is obtained. This test confirms the presence of the following in aqueous solution.
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Feb 1, 2014
Answer: Iodide $2I^- + Cl_2 \longrightarrow I_2 $ (violet) $+ 2Cl^-$$5Cl_2$ (excess) $+ I_2 ...
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Iodine reacts with $Na_2S_2O_3$ (aq) to give products which are
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Feb 1, 2014
Answer: colourless $I_2 + Na_2S_2O_3$ (sodium thiosulphate) $ \longrightarrow Na_2S_4O_6 $ (sod...
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Lead has been placed in the group I and II because
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Feb 1, 2014
Answer: It is partially soluble in water $PbCl_2$ is partially soluble in water and dissolves c...
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Suspended impurities from a colloidal solution of gum in water can be removed by
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Feb 1, 2014
Answer: filtration Suspended impurities can be removed from a colloidal solution by filtration...
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Which of the following can be enthalpy of neutralisation of a weak acid and a strong base?
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Feb 1, 2014
Answer: -56.1 KJ The magnitude of enthalpy of neutralsation of weak acid and strong base is alw...
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If enthalpy of neutralisation of $dil\; HCl$ and $NaOH\; (aq)$ is $x$ then enthalpy of neutralisation of dil HI and $Ba(OH)_2\; (aq)$ is
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Feb 1, 2014
Toolbox:Enthalpy of neutralisation of strong acid and strong base is always constant. Answer: x&nbs...
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Which of the following precipitates $K^+$ from its solution?
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Feb 1, 2014
Answer: sodium cobaltinitrite $Na_3[Co(NO_2)_6] $ (sodium cobaltinitrite) $+ 3KCl \longrightar...
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Which of the following is insoluble in dil. $HNO_3$ but soluble in aqua regia?
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Feb 1, 2014
Answer: HgS HgS is insoluble in dil. $HNO_3$ but soluble in aqua regia.$3HgS + 2HNO_3 + 6HCl \...
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When $H_2S$ is passed through an ammoniacal salt solution X, a white ppt. is obtained. Then X can be a
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Feb 1, 2014
Answer: zinc salt On passing $H_2S$ through zinc salt solution in the presence of $NH_4OH$, a...
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Distinguishing reagent between silver and lead salts
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Feb 1, 2014
Answer: dil HCl solution Both Pb and Hg form white ppt. of their chlorides. But $PbCl_2$ is sol...
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$H_2S$ in the presence of HCl precipitates group II but not group IV because
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Feb 1, 2014
Answer: HCl decreases the concentration of $S^{2-}$ ions Due to common ion effect, HCl suppres...
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Concentrated nitric acid is added before proceeding to test for group III members. This is to
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Feb 1, 2014
Answer: Convert ferrous ions to ferric ions To oxidise ferrous ion into ferric ion otherwise $...
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Mg is not precipitated in group V because
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Feb 1, 2014
Answer: None of these The concentration of $CO^{2-}$ ions is very low which does not prevent th...
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The ion that cannot be precipitated by both HCl and $H_2S$ is
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Feb 1, 2014
Answer: $Cu^{2+}$ All except $Cu^{2+}$ are precipitated both with HCl and $H_2S$. $Cu^{2+}$ is...
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Which of the following solution gives precipitate with $Pb(NO_3)_2$ but not with $Ba(NO_3)_2$ ?
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Feb 1, 2014
Toolbox:Since, $Na^+$ is more reactive than $Ba^{2+}$. So, $Ba^{2+}$ cannot displace $Cl^-$ from NaC...
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An aqueous solution of salt gives white precipitate with $AgNO_3$ solution as well as with dil $H_2SO_4$. It may be
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Feb 1, 2014
Answer: $BaCl_2$ $BaCl_2 + 2AgNO_3 \rightarrow 2AgCl \downarrow $ (white ppt.) $+ BaNO_3$$BaC...
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In a mixture having nitrite and nitrate can be destroyed by heating with
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Feb 1, 2014
Answer: Urea $NaNO_2 + H_2SO_4 \longrightarrow Na_2SO_4 + 2HNO_2$$2HNO_2 + NH_2CONH_2 \xrightar...
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For the test of halides, the soda extract is acidified with
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Feb 1, 2014
Answer: Dil $HNO_3$ Sodium carbonate extract is treated with Dil $HNO_3$ to destroy $CO_3^{2-}...
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Formation of purple colour on the addition of sodium nitroprusside to sodium carbonate extract indicates the presence of
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Feb 1, 2014
Answer: $S^{2-}$ $Na[(CN)_5NO]$ (Sodium nitroprusside) $ + Na_2S \xrightarrow{\Delta} Na_4[(CN...
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A salt solution is acidified with dil. $HCl$ and $BaCl_2$ solution is added. A white ppt. is formed. The salt contains
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Feb 1, 2014
Answer: $SO_4^{2-}$ White ppt. of $BaSO_4$ is insoluble in dil. $HCl$ and other mineral acids...
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Which one of the following cation will give a blue coloured ash when a piece of filter paper dipped in a solution containing its salt and $Co(NO_3)_2$ is burned?
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Feb 1, 2014
Answer: $Al^{3+}$ The filter paper ash test is substitute for cobalt nitrate charcoal cavity ...
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$H_2S$ and $SO_2$ can be distinguished by
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Feb 1, 2014
Answer: $Pb(CH_3COO)_2$ $Pb(CH_3COO)_2 + H_2S \longrightarrow PbS + 2CH_3COOH$$SO_2$ has no e...
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Acidified $K_2Cr_2O_7$ turns green by
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Feb 1, 2014
Answer: $SO_2$ $K_2Cr_2O_7$ turns green by $SO_2$ due to its reduction.$K_2Cr_2O_7 + H_2SO_4 + 3SO_...
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