Answer:
-3.82ºC is the freezing point of solution
Explanation:
We work with the Freezing point depression to solve the problem
ΔT = m . Kf . i
ΔT = Freezing point of pure solvent - freezing point of solution
Let's find out m, molality (moles of solute in 1kg of solvent)
15 g / 58.45 g/mol = 0.257 moles of NaCl
NaCl(s) → Na⁺ (aq) + Cl⁻(aq)
i = 2 (Van't Hoff factor, numbers of ions dissolved)
m = mol /kg → 0.257 mol / 0.250kg = 1.03 m
Kf = Cryoscopic constant → 1.86 ºC/m (pure, for water)
0ºC - Tºf = 1.03m . 1.86ºC/m . 2
Tºf = -3.82ºC
In balancing equations, we aim to get equal numbers of every type of atom on both sides of the equation, in order to satisfy the law of conservation of mass (which states that in a chemical reaction, every atom in the reactants is reorganised to form products, without exception). Therefore, let me walk you through question a:
<span>_Fe + _ H2SO4 --> _Fe2 (SO4)3 + _H2
First, take a stock-check of exactly what we currently have on each side (assuming that each _ represents a 1):
LHS: Fe = 1, H = 2, S = 1, O = 4
RHS: Fe = 2, H = 2, S = 3, O = 12,
There are two things to note here. Firstly, H2 (it should be subscript in reality) represents two hydrogen atoms bonded together as part of the ionic compound H2SO4 (sulphuric acid) - this two only applies to the symbol which is directly before it. Hence, H2SO4 only contains 1 sulphur atom, because the 2 applies to the hydrogen and the 4 applies to the oxygen. Secondly, the bracket before the 3 (which should also be subscript) means that there is 3 of everything within the bracket - (SO4)3 contains 3 sulphur atoms and 12 oxygen atoms (4 * 3 = 12).
Now let's start balancing. As a prerequisite, you must keep in mind that we can only add numbers in front of whole molecules, whereas it is not scientifically correct to change the little numbers (we could have two sulphuric acids instead of one, represented by 2H2SO4 (where the 2 would be a normal-sized 2 when written down), but we couldn't change H2SO4 to H3SO4).
The iron atoms can be balanced by having two iron atoms on the left-hand side instead of one:
2Fe </span>+ _ H2SO4 --> _Fe2 (SO4)3 + _H2
Now let's balance the sulphur atoms, by multiplying H2SO4 by 3:
2Fe + 3H2SO4 --> _Fe2 (SO4)3 + _H2
This has the added bonus of automatically balancing the oxygens too. This is because SO4- is an ion, which stays the same in a displacement reaction (which this one is). Take another stock check:
LHS: Fe = 2, H = 6, S = 3, O = 12
RHS: Fe = 2, H = 2, S = 3, O = 12
The only mismatch now is in the hydrogen atoms. This is simple to rectify because H2 appears on its own on the right-hand side. Just multiply H2 by 3 to finish off, and fill the third gap with a 1 because it has not been multiplied up. Alternatively, you can omit the 1 entirely:
2Fe + 3H2SO4 --> Fe2 (SO4)3 + 3H2
This is the balanced symbol equation for the displacement of hydrogen with iron in sulphuric acid.
For question b, I will just show you the stages without the explanation (I take the 3 before B2 to be a mistake, because it makes no sense to use 3B2Br6 when B2Br6 balances fine):
<span>B2 Br6 + _ HNO 3 -->_B(NO3)3 +_HBr
B2Br6 + _HNO3 --> _B(NO3)3 + 6HBr
B2Br6 + 6HNO3 --> _B(NO3)3 + 6HBr</span>
<span><span>B2Br6 + 6HNO3 --> 2B(NO3)3 + 6HBr</span>
Hopefully you can get the others now yourself. I hope this helped
</span>
Answer:
Infrared radiation → A) used to detect the location of objects
Microwaves → D) Used in radar and to heat food
Ultraviolet light → C)Given off by very hot objects, such as the sun Heat from warm objects
Visible light → B) All the radiation humans can see, ranging from red to violet
Explanation:
Microwaves have magnetic waves with very long lengths, greater than that of infrared light. These waves are produced through vibrations that produce heat, as the microwave is turned on, which allows the food to be heated. These waves are also used to provide communication on some types of devices.
Infrared radiation is a type of non-ionizing radiation that has a low frequency and therefore cannot be visualized, since it is not within a visible electromagnetic spectrum, having a frequency lower than red. It can be used to detect the licalization of objects and does not pose a health risk.
Ultraviolet radiation is extremely harmful to our body. It is characterized by radiation with very small wavelengths, less than 400nm. This type of radiation can be released by the sun and ultraviolet lamps.
Visible light refers to the simplest form of electromagnetic wave and covers all the radiation that our eyes can see, allowing different colors to be seen in the objects we observe according to the reorganization of atoms and molecules.
Answer:
36 KJ of heat are released when 1.0 mole of HBr is formed.
Explanation:
<em>By Hess law,</em>
<em>The heat of any reaction ΔH for a specific reaction is equal to the sum of the heats of reaction for any set of reactions which in sum are equivalent to the overall reaction:</em>
H 2 (g) + Br 2 (g) → 2HBr (g) ΔH = -72 KJ
This is the energy released when 2 moles of HBr is formed from one mole each of H2 and Br2.
Therefore, Heat released for the formation of 1 mol HBr would be half of this.
Hence,
ΔHreq = -36 kJ
36 KJ of heat are released when 1.0 mole of HBr is formed.
Answer:
The mass of magnesium that has been consumed, was 6.69 g
Explanation:
The reaction is this one:
3Mg (s) + N₂(g) → Mg₃N₂
3 moles of solid magnesium react with 1 mol of nitrogen, to make 1 mol of magnesium nitride.
If 9.27 grams of nitrogen react, we see that ratio is 1:1, so we make 9.27 grams of nitride.
Mass / Molar mass = Moles
9.27 g / 100.9 g/m = 0.092 moles
If we have 0.092 moles of nitride, ratio between Mg is 1:3 so, the rule of three will be:
1 mol of Nitride was produced by 3 moles of Mg (s)
0.092 moles of nitride were produced by, (0.092 .3)/1 = 0.275 moles
Mass og Mg = 24.3 g/m
Molar mass . Moles = Mass
0.275 m . 24.3g/m = 6.69 g
