Answer : The value of
is, -103.4 kJ
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The given main reaction is,

The intermediate balanced chemical reaction will be,
(1)

(2)

Now reversing and multiplying by 2 of reaction 1 and 2 then adding all the equations, we get :
(1)

(2)

The expression for
will be,



Therefore, the value of
is, -103.4 kJ
Answer:
My answer to the question is 0.00000051
In the physical properties, it is mentioned that the element has 4 valence electrons. The elements in the periodic table are arranged such that, the number of valence electrons present in the neutral atoms belonging to a particular group is equal to the group number.
Thus, the unidentified element can be best classified as a nonmetal in period 4
Ans C)
Answer:

Explanation:
N = Final mass of atom = 125 g
= Initial mass of atom = 16000 g
t = Time taken = 163.24 days
= Half life
We have the relation

The half life of the atom is
.
Answer:
Option C = object B by 1 gram per cubic cm.
Explanation:
Given data:
Mass of object A = 12 g
Volume of object A = 8 cm³
Mass of object B = 20 g
Volume of object B = 8 cm³
Densities = ?
Solution:
Density:
Density is equal to the mass of substance divided by its volume.
Units:
SI unit of density is Kg/m3.
Other units are given below,
g/cm3, g/mL , kg/L
Formula:
D=m/v
D= density
m=mass
V=volume
Symbol:
The symbol used for density is called rho. It is represented by ρ. However letter D can also be used to represent the density.
Density of object A:
d = m/v
d = 12 g/ 8 cm³
d = 1.5 g/cm³
Density of object B:
d = m/v
d = 20 g/ 8 cm³
d = 2.5 g/cm³
object b has high density.