IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

euracle

In some chemical reactions, heat, energy & water is released. Pls explain how it happens with some suitable examples. I also want to know when and at which condition do they release? How do we get them as a product?

Hats assured!!!

ridhima

this totally depends on the conditions in which reaction is being done

for heat and energy

suppose a process is carried out and the product formed is more stable than the reactant , then the product has less energy as compared 2 reactant and the excess energy is released in the for energy(heat , light,sound).

if product is less stable , then energy is required as the process is not spontaneous .

water

water is released in a rxn when oh and h ions combine i.e the reactants provide them during the course of rxn

it is noteworthy to mention that equilibrim constant for formation of water is in the range of about 10^9

so even if a little oh and h ion is produced the equilibrium will shift in the ffd

dir

and thus water is produced

do rate if u find it useful

euracle

I asked some examples and moreover how can i know that a product or a reactant is stable???

ridhima

take a simple eg of water
water disassociates to form oh and h ions. right
but this process is endothermic

why?
because see in the water molecules there is hydrogen bonding
the hydrogen of a molecule attracts the O atom in the molecule as it 4 unpaired e in its octed
thus the interaction bw the molecules is very lerge
ie the molecules are very strongly bonded so some energy is required for its disassociation

your doubt about how will i know which one is more stable
i would say that this is not the stage to understand
this requires multiple concepts from all fields of chem
don't get worried u'll learn more about it in +1
and even in 10th
best of luck

vibhav1991

lets see the example of hydration energy.
it is the amount of energy released when one mole of anhydrous salt combines with required number of water molecules so as to change into hydrated salt is enthalpy of hydration.

EXAMPLE-
CuSO4(s) + 5H2O ===gives CuSO4.5H2O(s) dH=-78.2KJ/mol

krishna.gopal

Another very good example is esterification reaction where acid plus alcohol gives ester plus water.

euracle

I have one more doubt.......

In the following reaction,

Fe + H₂O Fe₃O₄+ H₂

^{the product is Fe₃O₄+H₂}

^{pls explain how is Fe₃ formed when there is only one atom of Iron in the reactants? & how is that 4 atoms of oxygen r formed in the products when there is only 1 atom of oxygen in the reactants??}

^{Pls explain! I,m a bit weak!!!........}

^{hats assured} !!!

srujana

Chemical equations should be 'balanced' so as to make them 'chemically meaningful'

The equation you gave is an It is an unbalanced one.

$eq=Fe + H_2O\ \rightarrow Fe_3O_4 + H_2$

i.e, it doesn't follow the law of conservation of mass.

Hence we need to balance it.

Balancing the no. of oxygen atoms

$eq=Fe + 4H_2O\ \rightarrow Fe_3O_4 + H_2$

Balancing the no. of hydrogen atoms

$eq=Fe + 4H_2O\ \rightarrow Fe_3O_4 + 4H_2$

Balancing the no. of Fe atoms

$eq=3Fe + 4H_2O\ \rightarrow Fe_3O_4 + 4H_2$

The balanced equation should be,

$eq=3Fe + 4H_2O\ \rightarrow Fe_3O_4 + 4H_2$

While balancing the subscript cant be changed.

vibhav1991

srujana is right that every chemical reaction is balanced so as to follow law of conservation of mass and POAC.

computer001

its not abt balancing...its jus tht 3 atoms of Fe in the reaction environment combine to form a part of a single macro-molecule along with 4 oxygen atoms which on aggregation form the compoound as a whole(i mean in this case)

ridhima

hey
this fe304 is not the actual molecule that is formed

it is a mixture of fe0.fe2o3
for simplification it is written as fe304

vibhav1991

POAC means Principle Of Atomic Conservation.
In chemical reaction, atoms are conserved, so moles of atoms shall also be conserved. This is known as principle of atomic conservation.
This is helpful in solving stoichiometric calculations.
Eg-
KClO3(s)==gives KCl(s) + O2(g)
applying POAC===
moles of K atoms in KClO3=moles of K atoms in KCl

ridhima

the fe atoms are not 3
see when a rxn takes place it has a number of choices to for a product
i.e a number of products are formed but when we say that this product is formed we mean that it is the major product.ok
in this rxn both feo and fe2o3 have equal probabilty. this does not mean that there are 3 fe atoms in the molecule
it only means that both the products are formed
i hope u got it.

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