Answer: Option (b) is the correct answer.
Explanation:
Sublimation is defined as the process in which a solid substance changes directly into gaseous phase without undergoing into liquid phase.
For example, when naphthalene balls are kept in a trunk or cupboard then after some days or months it changes into gas. Hence, they become consumed.
Also during this process energy is being absorbed by the solid substance because for breaking bonds energy is always absorbed by a substance. Only then it can change into liquid or vapor state.
So, a chemical process in which energy is being absorbed by a reaction is known as endothermic reaction. And, if heat energy is being released by the reaction then it is known as an exothermic reaction.
Therefore, we can conclude that when a solid sublimes, a solid converts to a gas. This phase change is endothermic because energy is absorbed when the intermolecular forces break.
Answer:
-1268 kJ
Explanation:
The molar enthalpy of combustion of C6H6 is -3170 kJ/mol
2C6H6(g) + 15O2(g) → 12CO2(g) + 6H2O(g)
Therefore;
when 1 mole of C6H6 undergoes combustion, an energy of -3170 kJ/mol is released.
Therefore; for 0.40 mole
= 0.4 × -3170 kJ
= -1268 kJ
Answer:
8.085x10²¹ atoms
Explanation:
Atomic mass of Fe = 55.845 g/mol
it means ,
1 mole Fe = 55.845 g
1 mole = 6.02x10²³ atoms
so,
55.845g Fe has = 6.02x10²³ atoms
∴0.750 g Fe has = {(6.02x10²³ x 0.750)/55.84} atoms
=8.085x10²¹ atoms
The student needs to dilute the stock to get the proper concentration. And during the dilution, the molar number of solute will not change. So the volume of stock needed is 2*0.1/1.75=0.114 L. Then dilute to 2.00 L.
Missing question: what is the density of 53.4 wt% aqueous NaOH if 16.7 mL of the solution diluted to 2.00L gives 0.169 M NaOH?
Answer is: density is 1.52 g/mL.
c₁(NaOH) = ?; molarity of concentrated sodium hydroxide.
V₁(NaOH) = 16.7 mL; volume of concentrated sodium hydroxide.
c₂(NaOH) = 0.169 M; molarity of diluted sodium hydroxide.
V₂(NaOH) = 2.00 L · 1000 mL/L = 2000 mL; volume of diluted sodium hydroxide.
Use equation: c₁V₁ = c₂V₂.
c₁ = c₂V₂ / V₁.
c₁ = 0.169 M · 2000 mL / 16.7 mL.
c₁(NaOH) = 20.23 M.
m(NaOH) = 20.23 mol · 40 g/ml.
m(NaOH) = 809.53 g.
The mass fraction is the ratio of one substance (in this example sodium hydroxide) with mass to the mass of the total mixture (solution).
Make proportion: m(NaOH) : m(solution) = 53.4 g : 100 g.
m(solution) = 1516 g in one liter of solution.
d(solution) = 1516 g/L = 1.52 g/mL.
