With method 2 I will work out the rate order of the metals.
The equations below are the ionic and
The ionic equations below show which ions are taking part in my reactions
Mg (aq) +HCl (aq) = MgCl (aq) + H2 (aq)
Mg+ + Cl_ =Mg +Cl_
Zn (aq) + HCl (aq) = ZnCl (aq) + H2(aq)
Zn ++Cl _=ZnCl
Al (aq) + HCl (aq) = AlCl (aq) ) + H2(aq)
Al ++ Cl _ =AlCl
Background research
Chemical reactions require varying lengths of time depending on the characteristics of the reactants and the conditions under which the reaction is taking place
Most of the chemical reactions have different rate of reaction and their rate of reaction is related to many factors including
The different states have different rate of reactivity .The substance in gaseous state will be more reactive as compared to liquid and solid state of matter.
Some substance are organic in nature and others inorganic .The organic substances are comparatively more volatile and reactive at low temperature as compared to inorganic compounds. The organic compounds are mostly non polar where as the inorganic compounds are polar. It is the polarity which greatly affects the rate of reaction.
The atmospheric pressure is also an important condition which facilitates the reaction. Some reactions go to proceed at low pressure but others need high pressure. Hydrogen and oxygen react under normal pressure of 1atm to make water whereas hydrogen and nitrogen react under 200atm to make ammonia.
The percentage purity is an important condition to overcome .the rate of reaction of pure samples take part speedily in the reaction because of their free movement in three dimensions, whereas the impure sample show sluggish reaction because of the impurity hindrance in the free collision and movement.
There are various sources of energy which affect the reactivity in different ways like solar ,electric ultrasonic ultraviolet, infra red and heat temperature. Among all these sources the most important source is that one which can cause more effective collision among the particles.
Energy activating tools -the energy activating tools includes hormones enzymes and catalysts which indirectly control the energy of activation to overcome the sack bags in the reaction.
A normal level of PH is significant for normal reaction .if the PH is undergoing change the reaction will be badly affected even if all the other conditions are completely fulfilled .
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-ionic state of the system
- Ionic state of matter is important to favour the reaction as compared to non ionic state because the ionic state makes the reaction faster and quicker.
- -area of system provided
The area and size of the particles are highly effective in the reaction, the particle with smaller size in the form of powder are more reactive as compared to the crystal form of substance.
The studying of rate of reaction is very important. Rate of a reaction is the change in concentration of reactant to products and vice versa in a given time. Rate is the change of reactant to products in unit time. Time factor is very significant in determining the completion of reaction.
The rate of reaction can be affected by many important factors, namely temperature, concentration of reactants (or pressure for gases) presence of catalyst or surface area of solid substances.
Effect of Temperature
At higher temperatures the particles have energy therefore can collide to break existing bonds and make new recombinations of product particles. The minimum energy needed for an effective collision is called activation energy .Activation energy can also be defined as the energy that an atomic system must acquire before a process can occur.
Increasing the temperature of the system has the following effects
- increases the range of kinetic energies
- increases the average kinetic energy
- increases the population of particles with more than the activation energy
- increase the rate of collision
- Increase the average movement of particles in three dimensions.
The effect of temperature on the oxidation of some hydrocarbons can very clearly be understood by heating methane under different range of temperatures
CH4 +O2= CO2+HO (70 0 C)
(60) CH4 +O2= CO2+H2O
The effect of temperature can be studied by measuring the amount of CO2 produced at the end of reaction .at higher temperatures less concentrations of CO2 is produced and at lower temperatures high volume of CO2 is produced.
This concentration of CO2 can be measured by dissolving or diffusing it in the dilute solution of calcium hydroxide Ca (OH) 2.which is turned milky.
CO2+Ca (OH)2=CaCO3+H2O
The CaCO3 will be a white precipitate
Concentration
As a reaction proceeds its concentration falls therefore the rate also falls until there is no reactant left putting a stop to the reaction. The concentration falls because there is a change in number of particles in a unit volume hence the number of collisions per unit. If no of collections fall then reaction rate will change
The rate equation summarizes mathematically the effect of the concentration of reactant on reaction rate
rate concentration
Rate=k [concentration]
Therefore a rate equation involving three reactants can be written as
r = [A] [B] [C]
K is put into the equation as a proportionality constant .this the below equation
R =K [A] 0 [B] 1 [C] 2
The k has no variable unit and depends on the order of reaction it moreover helps balanced the equation in equilibrium
Where the square brackets denotes molar concentration
Rate of a reaction is always measured in mol dm-3
Powers to which each concentration is raised are called orders. The orders with respect to A is a, the order with respect to B is b.
The order of a reaction does not follow from its stoichoimetric equation. The reaction between bromate (V) ions and hydrogen ions give bromine is represented by the equation
Br03 (aq) +5br-(aq) +6h+(aq)=3br2+3h20
Zero order reactions
In a zero order reaction rate does not depend on the concentration of the reactant a plot of the concentration of the reactant [A] against time has the form shown in figure below. The graph is a straight line as the reaction proceeds at the same rate whatever the concentration
The rate equation for a zero order reaction is
Rate =k [A]
The rate constant has the unit concentration time -1
For order zero the rate coefficient has the units mol dm-3s-1
First order reactions
In first order reaction the rate is proportional to the concentration.
If the reaction
A=Products
Is first order the rate equation will be
Rate= k [A]
Since the rate is proportional to concentration of A when half of A has reacted the rate will be half the initial rate. When three quarters of a have reacted the rate will be one quarter of the initial rate. The graph of A against time is shown below in the graph for a first order reaction .there is a curve because the time it takes for the concentration of the reactant to be halved (the half-life) is constant whatever the concentration.
Second order reactions
Graphs for second order reactions are a curve but much deeper than first order one and the half life is not constant it will increase dramatically as reaction proceeds.
The units of the rate coefficient depend on the global order of reaction:
- For order zero, the rate coefficient has units of mol dm-3s-1
- for order one the rate coefficient has units of s-1
- For order two the rate coefficient has the units mol-1dm3s-1
For order n the rate coefficient has the units of mol 2-n dm6-3ns-1
