Recent questions tagged chemical-kinetics

(i) A chemical reaction $2A \to 4B + C$ in gas phase occurs in a closed vessel. The concentration of $B$ is found to increase by $5 \times 10^{-3}\; mol L^{-1}$ in $10$ seconds, Calculate (a) the rate of appearance of B (b) the rate of disappearance of A. (ii)The activation energy of first order reaction at $300\;K$ is $60 kJ/mol$ . In the presence of a catalyst, the activation energy gets lowered to $50 kJ/mol$ at $300K$. How many times the reaction rate changes in presence of a catalyst at the same temperature?(iii) Define Threshold energy and activation energy. How they are related?

asked Nov 29, 2016 by meena.p

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Explain giving reasons: (i) Transition metals and many of their compounds show paramagnetic behaviour. (ii) The enthalpies of atomisation of the transition metals are high. (iii) The transition metals generally form coloured compounds. (iv) Transition metals and their many compounds act as good catalyst.

asked Nov 29, 2016 by meena.p

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Distinguish between rate expression and rate constant of a reaction. (ii) Can a reaction have zero activation energy ? explain (iii) Is the enthalpy of a reaction altered by a catalyst

asked Nov 29, 2016 by meena.p

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Decomposition of phosphine $(PH_3)$ at $120^{\circ}C$ proceeds according to the equation: $4PH_3(g) \to P_4(g) + 6H_2(g)$ It is found that this reaction follows the following rate equation: Rate $= k[PH_3]$ The half-life of $PH_3$ is $37.9\;s$ at $120^{\circ}C.$ (i) How much time will be required for $\large\frac{3}{4}$ of $PH_3$ to decompose? (ii) What fraction of the original amount of $PH_3$ will remain undecomposed after 1 minute?

asked Nov 22, 2016 by meena.p

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15.0 g of unknown molecular material was dissolved in 450 g of water. The resulting solution was found freezes at $−0.34^{\large\circ}$C. What is the molar mass of this material? ($K_f$ for water = $1.86 \;K\; kg \;mol^{−1}$)

asked Nov 16, 2016 by meena.p

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In a hydrolysis reaction, $5\;g$ ethyl acetate is hydrolysed in presence of dilute HCl in $300\; minutes$. If the reaction is of first order and the initial concentration of ethyl acetate is $22\;g/L$, calculate the rate constant of the reaction.

asked Nov 16, 2016 by meena.p

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Consider the decomposition of hydrogen peroxide in alkaline medium which is catalyzed by iodide cons . $2H_2O_2 \qquad \underrightarrow{-OH} \qquad 2H_2O+O_3$ This reaction takes place in two steps as given below Step I:$H_2O_2+I^{-} \to H_2O+I_0^{-}$ (slow) Step II:$H_2O_2+IO^{-} \to H_2O+I^{-}+O_2$ (fast) a) Write the rate law expression and determine the order of reaction w.r.t $H_2O_2$ b) What is the molecularity of each individual step ?

asked Nov 15, 2016 by meena.p

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Distinguish between rate expression and rate constant of a reaction

asked Nov 10, 2016 by meena.p

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a)i)The resistance of a conductivity cell containing $0.001\;M\; KCl$ solution at $298\;K$ is $1500 \Omega$. What is the cell constant, if the conductivity of $0.001\;M\; KCl$ solution at $298\;K$ is $0.146 \times 10^{-3}\;S\;cm^{-1}$? ii)Explain with one example each the terms weak and strong electolytes iii)The standard reduction potential values of three metallic cations $X,Y, Z$ are $+0.52, − 3.03, − 1.18 V$ respectively. What will be the order of reducing power of the corresponding metals? b) Distinguish between rate expression and rate constant of a reaction

asked Nov 10, 2016 by meena.p

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(I)(a) Calculate the boiling point of a solution containing $0.61\;g$ of benzoic acid in $5\; g$ of $CS_2$ .Assuming $84\%$ dimerisation of acid. The boiling point and $K_b$ of $CS_2$ are $46.2^{\circ}0C$ and $2.3\; K\; Kg \;mol^{-1}$ respectively. (b) State Raoult's law for the solution containing non-volatile solute. Give its mathematical expression also. (II) A solution of $KMnO_4$ on reducing yields either a colourless solution or a brown precipitate or a green solution depending on $PH$ of the solution . What different stages of the reduction do these represent and how are they carried out ?

asked Nov 10, 2016 by meena.p

1 answer

(a)Define the following terms : (i) Mole fraction (ii) Ideal solution (b) For the reaction $A \to B$ ,the rate of reaction becomes twenty seven times when the concentration of A is increased three times . What is the order of the reaction ?

asked Nov 9, 2016 by meena.p

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A solution of $KMnO_4$ on reducing yields either a colourless solution or a brown precipitate or a green solution depending on $PH$ of the solution . What different stages of the reduction do these represent and how are they carried out ?

asked Nov 7, 2016 by meena.p

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For the reaction $A \to B$ ,the rate of reaction becomes twenty seven times when the concentration of A is increased three times . What is the order of the reaction ?

asked Nov 3, 2016 by meena.p

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Nitric oxide $NO,$ reacts with oxygen to produce nitrogen dioxide $2 NO(g)+O_2(g) \to 2NO_2(g)$ The rate law for this reaction is : $Rate = k[NO]^2 [O_2]$ Propose a mechanism for the reaction.

asked Oct 27, 2016 by meena.p

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(a)The rate constant for a reaction of zero order in A is $0.0030\;mol L^{-1}S^{-1}$ How long will it take for the initial concentration of A to fall from $0.10\;M$ to $0.075\;M$ ? (b)What type of colloidal sols are formed in the following : (i) Sulphur vapours are passed through colled water (ii) White of an egg is mixed with water . (iii) Soap solution

asked Oct 25, 2016 by meena.p

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What type of colloidal sols are formed in the following : (i) Sulphur vapours are passed through colled water (ii) White of an egg is mixed with water . (iii) Soap solution

asked Oct 24, 2016 by meena.p

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(i)What is the freezing point of $0.4 $ molal solution of acetic acid in benzene in which it dimerises to the extent of $85\%$ Freezing point of benzene is $278.4 \;k$ and its molar heat of fusion is $10.042\;kj\; mol^{-1}$ (ii) Write balanced chemical equation for the following reactions : (a) Thermal decomposition of ammonium dichromate. (b) Reaction of $Cl_2$ with cold and deleted NaOH (c) When phosphine is passed through mercuric chloride solution .

asked Oct 24, 2016 by meena.p

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Write balanced chemical equation for the following reactions : (a) Thermal decomposition of ammonium dichromate. (b) Reaction of $Cl_2$ with cold and deleted NaOH (c) When phosphine is passed through mercuric chloride solution .

asked Oct 19, 2016 by meena.p

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Account for the following : (i) Transition elements show highest oxidation state in their oxides thanfluorides. (ii) Cu has positive electrode potential in the first transition series. (iii) Ionisation enthalpy of lanthanides is higher than actinides. (iv) Potassium dichromate is a good oxidising agent in acidic medium. (v) Actinides show more number of oxidation states than lanthanides.

asked Oct 18, 2016 by meena.p

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Which of the following statement(s) is/are correct?

asked Jan 18, 2016 by meena.p

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For a complex reaction ___________

asked Sep 24, 2015 by meena.p

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Mark the incorrect statement :

asked Sep 24, 2015 by meena.p

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Which of the following statement is not correct for the catalyst ?

asked Sep 24, 2015 by meena.p

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During decomposition of an activated complex

asked Sep 24, 2015 by meena.p

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The value of rate constant of a pseudo first order reaction _____________

asked Sep 24, 2015 by meena.p

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A first order reaction is $50\%$ completed in $1.26 \times 10^{14}\;s$ . how much time would it take for $100 \%$ completion ?

asked Sep 24, 2015 by meena.p

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Activation energy of a chemical reaction can be determined by __________

asked Sep 24, 2015 by meena.p

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In the presence of a catalyst, the heat evolved or absorbed during the reaction

asked Sep 24, 2015 by meena.p

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The role of a catalyst is to change ______________

asked Sep 24, 2015 by meena.p

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$T_{50} $ of first order reaction is 10 min storing with $10\; mol^{-1}$ rate after 20 min is

asked Sep 24, 2015 by meena.p

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According to the law of mass action, rate of a chemical reaction is proportional to

asked Sep 24, 2015 by meena.p

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Units of rate constants for first and zero order reactions in term of morality M unit are respectively

asked Sep 24, 2015 by meena.p

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The decomposition of HI on the surface of gold is

asked Sep 24, 2015 by meena.p

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In Arrhenius equation $k= Ae^{- \in a /RT}$, factor $e^{-\in a/RT}$ is known as

asked Sep 24, 2015 by meena.p

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If concentration of reactant is increased by 'm'. then k becomes

asked Sep 24, 2015 by meena.p

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$\in$ Threshold can never be :

asked Sep 24, 2015 by meena.p

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Unit of frequency factor(A) is :

asked Sep 24, 2015 by meena.p

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The inversion of cane sugar into glucose and fructose is

asked Sep 24, 2015 by meena.p

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Number of moles of a substance present in liter volume is known as

asked Sep 24, 2015 by meena.p

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The number of molecules of the reactants taking part in a single step of the reaction tells about :

asked Sep 24, 2015 by meena.p

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Rate of a chemical reaction can be kept constant by

asked Sep 23, 2015 by meena.p

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The half life period of a rectangle is constant for :

asked Sep 23, 2015 by meena.p

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The role constant of a reaction does not depend upon

asked Sep 23, 2015 by meena.p

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Radioactive disintegration is an example of :

asked Sep 23, 2015 by meena.p

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molecularity of a reaction is :

asked Sep 23, 2015 by meena.p

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The specific rate constant of a first order reaction depends on

asked Sep 23, 2015 by meena.p

3 answers

The hypothetical reaction $A_2+B_2\to 2AB$ follows the following mechanism $A+B_2 \to AB+B; A+B\to AB$

asked Sep 23, 2015 by meena.p

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For a single step reaction $A+2B \to Products$ the molecularity (ie)

asked Sep 23, 2015 by meena.p

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Second order rate constant is usually expressed as

asked Sep 23, 2015 by meena.p

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The hydrolysis of ethyl acetate is a reaction of $CH_3COOC_2H_5 +H_2O \to CH_3COOH +C_2H_5OH$

asked Sep 23, 2015 by meena.p

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