reacts very slowly with cold
water, but rapidly in boiling
water, and very vigorously
react with acids. Very poor
reaction with steam.
may react with some strong
Going from the bottom to the top of the table the metals:
increase in reactivity;
lose electrons (oxidize) more readily to form positive ions;
corrode or tarnish more readily;
require more energy (and different methods) to be separated from their ores;
become stronger reducing agents (electron donors).
There is no unique and fully consistent way to define the reactivity series, but it
is common to use the three types of reaction listed below, many of which can be
performed in a high-school laboratory (at least as demonstrations).
Reaction with water and acids
hydrogen and the metal hydroxide:
2 Na (s) + 2 H
such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a
metal salt, such as iron(II) sulfate:
An iron nail placed in a solution of copper sulfate will quickly change colour as
metallic copper is deposited and the iron is converted into iron(II) sulfate:
Fe (s) + CuSO
tetrachloride, forming magnesium chloride in the process:
2 Mg (s) + TiCl
metallic potassium by the reduction of potassium chloride with sodium at 850 °C.
Although sodium is lower than potassium in the reactivity series, the reaction can
proceed because potassium is more volatile, and is distilled off from the mixture.
Na (g) + KCl (l)
→ K (g) + NaCl (l)
Comparison with standard electrode potentials
The reactivity series is sometimes quoted in the strict reverse order of standard
electrode potentials, when it is also known as the "electrochemical series":
Li > K > Sr > Na > Ca > Mg > Al > Mn > Zn > Cr(+3) > Fe > Cd > Co > Ni >
Sn > Pb > H > Cu > Hg > Ag > Pd > Ir > Pt > Au
The positions of lithium and sodium are changed on such a series; gold and
platinum are in joint position and not gold leading, although this has little practical
significance as both metals are highly unreactive.
Standard electrode potentials offer a quantitative measure of the power of a
reducing agent, rather than the qualitative considerations of other reactive series.
However, they are only valid for standard conditions: in particular, they only apply to
reactions in aqueous solution. Even with this proviso, the electrode potentials of
lithium and sodium – and hence their positions in the electrochemical series – appear
anomalous. The order of reactivity, as shown by the vigour of the reaction with water
or the speed at which the metal surface tarnishes in air, appears to be
potassium > sodium > lithium > alkaline earth metals,
the same as the reverse order of the (gas-phase) ionization energies. This is
borne out by the extraction of metallic lithium by the electrolysis of a eutectic
mixture of lithium chloride and potassium chloride: lithium metal is formed at the
cathode, not potassium.
In a reactivity series, the most reactive element is placed at the top and the least
electrons and form positive ions.
A reactivity series of metals could include any elements. For example:
A good way to remember the order of a reactivity series of metals is to use the
Children Make A Zebra Ill ConstantlySniffing Giraffes.
Observations of the way that these elements react with water, acidsand steam
enable us to put them into this series.
The tables show how the elements react with water and dilute acids:
Note that aluminium can be difficult to place in the correct position in the
reactivity series during these experiments. This is because its protective aluminium
oxide layer makes it appear to be less reactive than it really is. When this layer is
removed, the observations are more reliable.
Non-metals in the reactivity series
It is useful to place carbon and hydrogen into the reactivity series because these
elements can be used to extract metals.
Here is the reactivity series including carbon and hydrogen:
Note that zinc and iron can be displaced from their oxides using carbon but not
We have explained that a chemical reaction will not occur until substances
(reactants) receive enough energy (activation energy) to break chemical bonds. This
allows atoms to redistribute themselves to form new bonds and thus form new
substances (products). The activation energy needs to be thought of as a barrier to be
overcome. If the bonds between the reactants are strong, greater activation energy is
required to initiate a chemical reaction; if the bonds are weak, less activation energy
In the first stage of a chemical reaction, the enthalpy of the reactants increases
through some form of energy transfer. Therefore, the total energy of the reactants
increases by the amount of the activation energies. At this point, bonds are broken. In
the next stage, new bonds are made in the formation of the products. The total energy
of the products (i.e. the sum of the enthalpies) may be greater than, or less than, that
of the reactants. When the total energy of the products is less than that of the
reactants, the chemical reaction is called an ‘exothermic reaction’, and when the total
energy of the products is more than that of the reactants, the chemical reaction is
called an ‘endothermic reaction’.
To be consistent with the law of conservation of energy, in an exothermic
reaction, excess energy is transferred to the surrounding materials that do not take
part in the reaction (the surrounding environment): the environment heats up.
In an endothermic reaction, energy is taken from the surrounding environment:
the environment (the surrounding substance) cools down.
The different types of chemical reaction are shown in Figure 1. Note that the
total energy of the whole system (surrounding environment–reactants–products)
remains constant before and after the reaction, whereas this is not true for the total
energies of the reactants compared to the products.
Energy diagram for an exothermic reaction
Energy diagram for an endothermic reaction
A good example of an endothermic reaction is the use of an instant icepack.
sprains. A typical icepack contains the ionic compound ammonium nitrate salt
), which reacts with water. In solution (the ionic solid dissolved in water),
the ionic bonds are broken, freeing up ammonium ions (NH
). During the reaction, energy is taken from the surrounding environment (for
example, the ankle), thus cooling it down. The equation for the reaction is:
Many foods we eat undergo exothermic reactions and literally warm us up.
O) as the products. The energy given off assists in the maintenance of a
The equation for the reaction is:
It is important to note that, in this reaction, the reactants involve more than two
reaction produces six molecules each of carbon dioxide and water. As an exercise,
convince yourself of the law of conservation of atoms by determining that the total
number of each type of atom is the same on each side of the chemical equation.
Chemical reactions vary greatly in the speed at which they occur. Some are
Reaction Rate for a given chemical reaction is the measure of the change in
concentration of the reactants or the change in concentration of the products per unit
The speed of a chemical reaction may be defined as the change in
concentration of a substance divided by the time interval during which this change is
For a reaction of the form A+B
of the change in concentration of any of its components
reactant always decreases with time, so
Δ[A]and Δ[A] are both negative. Since
negative rates do not make much sense, rates expressed in terms of a reactant
concentration are always preceded by a minus sign to make the rate come out
Consider now a reaction in which the coefficients are different:
It is clear that [B] decreases three times as rapidly as [A], so in order to avoid
ambiguity when expressing the rate in terms of different components, it is customary
to divide each change in concentration by the appropriate coefficient:
it was found that the rate of formation of N
was 0.27 mol L
O] = 6/2
], so the rate of
) = 0.81 mol L
b) 4 moles of NH
are consumed for every 2 moles of N
formed, so the rate of
disappearance of ammonia is
2 × (0.27 mol L
) = 0.54 mol L
acceptable to express this last value as a negative number.
Most reactions slow down as the reactants are consumed. Consequently, the
rates given by the expressions shown above tend to lose their meaning when
measured over longer time intervals
Δt. Note: Instantaneous rates are also known as
Thus for the reaction whose progress is plotted here, the actual rate (as
measured by the increasing concentration of product) varies continuously, being
greatest at time zero. The instantaneous rate of a reaction is given by the slope of a
tangent to the concentration-vs.-time curve.
An instantaneous rate taken near the beginning of the reaction (t = 0) is known
as an initial rate (label (1)here). As we shall soon see, initial rates play an important
role in the study of reaction kinetics. If you have studied differential calculus, you
will know that these tangent slopes are derivatives whose values can very at each
point on the curve, so that these instantaneous rates are really limiting rates defined
If you do not know calculus, bear in mind that the larger the time interval
the smallerwill be the precision of the instantaneous rate.
During the course of the reaction shown below, reactants A and B are
consumed while the concentration of product AB increases. The reaction rate can be
determined by measuring how fast the concentration of A or B decreases, or by how
fast the concentration of AB increases.
Figure 1. The above picture shows a hypthetical reaction profile in which the
Looking at Figure 1 above, we can see that the rate can be measured in terms
of either reactant (A or B) or either product (C or D). Not all variables are needed to
solve for the rate. Therefore, if you have the value for "A" as well as the value for "a"
you can solve for the reaction rate.
You can also notice from Formula 1 above that, the change in reactants over
the change in time must have a negative sign in front of them. The reason for this is
because the reactants are decreasing as a function of time, the rate would come out to
be negative (because it is the reverse rate). Therefore, putting a negative sign in front
of the variable will allow for the solution to be a positive rate.
A rate law is an expression which relates that rate of a reaction to the rate
proportionality constant for a given reaction. The general rate law is usually
As you can see from equation 2 above, the reaction rate is dependent on the
other factors that can influence the rate of reaction. These factors include temperature
and catalysts. When you are able to write a rate law equation for a certain reaction,
you can determine the Reaction Order based on the values of s and t.
If you were to observe a chemical reaction to occur in two different setting
(one at a higher temperature than the other), you would most likely observe the
reaction occuring at a higher temperature to have a higher rate. This is because as you
increase the temperature, the kinetic energy of the reactants increase, allowing for
more collisions between the molecules. This, therefore, allows for products to be
formed faster. A simple rule of thumb that can be used is: for every 10°C increase,
the reaction rate doubles.
However, increasing the temperature will not always increase the rate of the
reaction. If the temperature of a reaction were to reach a certain point where the
reactant will begin to degrade, it will decrease the rate of the reaction.
As stated in the note above, the rate constant, k, is dependent on the
temperature of which the reaction takes place. This can be seen through the Arrhenius
Equation shown below:
As you can see from equation 3, the rate constant kk is dependent on the
temperature (in Kelvins) and also the Activation energy, E
"A" in the
equation represents a pre-exponential factor that has the same units as k. Finally, R is
the universal gas constant.
Catalysts are a class of molecules which lower the activation energy (E
required for reactants to collide and form products. They are not consumed in the
progressing forward. Thus, catalysts increase the rate of reaction. The most common
type of catalyst is the Enzyme Catalyst. In chemical reactions, products are formed
when reactants collide with one another. Enzymes allow for reactants to collide in
perfect orienation making the reaction more effective in forming products.
The reaction rate for a given reaction is a crucial tool that enables us to
calculate the specific order of a reaction. The order of a reaction is important in that it
enables us to classify specific chemical reactions easily and efficiently. Knowledge of
the reaction order quickly allows us to understand numerous factors within the
reaction including the rate law, units of the rate constant, half life, and much more.
Reaction order can be calculated from the rate law by adding the exponential values
of the reactants in the rate law. It is important to note that although the reaction order
can be determined from the rate law, there is no relationship between the reaction
order and the stoichiometric coefficients in the chemical equation.
does not need to be an integer.
As shown in Formula 5, the complete reaction order is equal to the sum of "s"
and "t." But what does each of these variables by themself mean? Each variable
represents the order of the reaction with respect to the reactant it is placed on. In this
certain situation, s is the order of the reaction with respect to [A] and t is the order of
the reaction with respect to [B].
Here is an example of how you can look at this: If a reaction order with respect
to [A] was 2 (s = 2) and [B] was 1 (t = 1), then that basically means that the
concentration of reactant A is decreasing by a factor of 2 and the concentration of [B]
is decrease by a factor of 1.
So if you have a reation order of Zero (s + t = 0), this basically means that the
concentration of the reactants does not affect the rate of reaction. You could remove
or add reactants to the mixture but the rate will not change.
A list of the different reaction rate equations for zero-, first-, and second-order
reactions can be seen in Table 1. This table also includes further equations that can be
determine by this equation once the order of the reaction is known (Half life,
integrated rate law, etc.)