Measurement of reaction rate

Measurement of reaction rate

Reaction rate are measured kinetically at standard temperature at a given condition. A mixture of reaction with already known composition is prepared and thermo stated. Concentration is decreased of reacting substances, or formation of reaction product with certain time interval is measured as function of time by some appropriate calculation and parameter. From the above concentration-time data,kinetic property of the system can be decreased withhelpof certain principle which may be developing as the fallowing way. Dependence of rate of reaction with temperature can be obtained by repeating this process with optimum temperature which is needed in that system.

The main way of concentration difference occurring a particular reaction is removal of given sample from the system at various interval of time,reaction becomes stops and the sample can be analyzed either by structure or other means to determine the concentration of either reactant or product. All chemist were fallowed the measure of change of concentration of either reactant or product by applying the physical properties which can be changed with time. Ingaseousreaction with volume change, that property most support observed a change in pressure at constant volume or variation of pressure in case of constant volume in a given system. Similar types of rule is applied in liquid system which is referred as automatically. Other physical factors used in suitable condition are spectroscopy, conductivity, calorimetric, gas evolution, viscosity, index variation, light scattering, mass spectroscopy etc.

The way of determining rate of reaction as kinetics is a forward pathway. The reaction is changewith time, so it must be determined by experimentally as well as theoretically by expressing in it tabulated form. From the observation with data, we can easily calculate the rate of reaction by fallowing algebraic relation or graphic way. What follows inreaction is principle way and reference of measuring rate of reaction. Change in time can be measured easily by using stopwatch or any other suitable devices. Butmeasuringchange in concentration of product or reactant are complicated process. The change of concentration in a system can generally be acquired into two ways. First one is by controlling decrease of reactant over a time and second one is by controlling formation of product over a time.

Method of measurement of concentration

For gaseous experiment burets are used to measure the change in volume produced different times which relates with the volume changes in concentration. Very small sample of reaction can be removed by chemist from a reaction mixture a different time and concentration can be analyzed by following different form of titration method.

• The use of spectrometer can be included in addition method to observe the concentration using Beer’s law.Veryfast reaction can be measured by using advanced technique like computer with laser magnetic resonance(LMR).
• Measuring reaction rate are related in supplemental information such a role of catalyst, concentration of reactants, characteristics ofrateof chemical reaction.

Measuring reagents Versus product

Measuring reagents versus product does not depend upon concentration change with reactant product because there is no effect on overall reaction. When concentration of reactant decrease, the concentration of product increase in equal amount within same time.Decreaseofconcentrationof reactant and increase in concentration of reactant is just opposite and equal insignwhich crosses is other seems to be no effect on overall reaction. Stoichiometry is one factor swhich is depends upon overall reaction.

It is noticed that change in concentration process can be gently solved by taking different physical or chemical properties. That may be phased difference, reduction potential etc. of reagent or product involved in that particular reaction. The main focus is stoichiometry coefficient and we should turn our attention towards it.

Unique average rate of reaction

A reaction rate can be monitoring by selecting quit different type of product and reactant with suitable condition.

Give a reaction

aA + bB$$\longrightarrow$$ cC + dD

reaction rate = $$-\frac{1.(dA)}{a.dt}$$ = $$-\frac{1.(dB)}{b.dt}$$= $$\frac{1.(dC)}{c. dt}$$=$$\frac{1.(dD)}{d.dt}$$

this formula can be also expressed as rate of reaction = $$-\frac{1}{a}$$ [rate of decrease in concentration of A].

=$$-\frac{1}{b}$$[rate of decrease in concentration of B].

=$$\frac{1}{c}$$[rate of decrease in concentration of C].

=$$\frac{1}{d}$$[rate of decrease in concentration of D]

Although the concentration of reactant A,B and product C and D increase or decrease with different rate, the average rate of reaction is only one. The unique rate can get by choice any one rate and divide by stoichiometry coefficient. When reaction has the formula

C_{R1R1 + ........+ CRn}R_{n →} C_p1P₁+.............+C_pnP_n

The genral way in which unique reaction rate form is rate of reaction =$$-\frac{1 d(R)}{CR1dt} $$ = $$\frac{1. (dRn)}{CRn.dt}$$=$$\frac{1. (dP1)}{CP1.dt}$$ =$$\frac{1. (dPn)}{CPn.dt}$$

Average and instantaneous reaction rate:

Reaction rate is general expression of change in concentration of reactants or product per unit time. There are usually two forms of reaction rates one is called average rate of reaction which can be represented by $$\frac{d(conc)}{dt}$$, another one is instantaneous rate of reaction denoted rate

Lim_{dt=0 $$\frac{d(concentration)}{dt}$$}

The average rate of reaction, as the name suggest is an average rate, which can be observed by concentration over the time period e.g. 0.3M/20 minutes. This is just approximation of rate of reaction with time intervals. It does not say that reaction should have the specific rate throughout interval time. Interval rate is not necessary to give accurate value. Instantaneous rate of reaction is those rate which is measured with different time interval so it seems that instantaneous reaction is more accuracy than average rate of reaction. Instantaneous rate can be calculated by plotting graph at slope of tangent line at only specific point which corresponds to the time of interest. By alternatively, experimenter can measure the change in concentration of reaction or product with very short time interval. Repetition of measurement gives more accurate value.

Initial rate of reaction:-

The reaction which is measured before the reaction start is called initial rate. Initial rate also can observe graphically like instantaneous rae. To take reading of initial rate, experimenter must bring reagent together and should measure rate quickly as far as possible. To measure it, reaction rate should be plot graphically at time ‘t’=0.

Reference

Bahl, B.S.Essential of Physical Chemistry. New Delhi: S. Chand & Company Pvt. Ltd, 2005.

Bahl, B.S., Arun Bahl and G.D. Tuli.Essential of Physical chemistry. New Delhi: S. Chand & Company Pvt. Ltd., 2005.