Answer:
32 days
Explanation:
Half life is the amount of time it takes to get to half of the starting concentration / amount.
Starting amount = 250 g
Half life = 8 days
Amount left = 15.625 g
How many days ? That is, how many half lives....
After first Half life;
Amount left = 250 / 2 = 125 g
After second half life;
Amount left = 125 / 2 = 62.5 g
After third half life;
Amount left = 62.5 / 2 = 31.25 g
After fourth half life;
Amount left = 31.25 g / 2 = 15.625 g
That is the radioactive iodine - 131 went though four half lives.
How many days = Number of half lives * Half life
How many days = 4 * 8 = 32 days
To create the liquid and superfluid states you cool down helium gas to a few degrees above absolute zero
Answer:
a) ΔU = 370 KJ
b) Endothermic
Explanation:
a)
The change in energy of the mixture can be given by first law of thermodynamics as:
ΔQ = ΔU + W
ΔU = ΔQ - W
where,
ΔQ = change in heat energy of system
ΔU = Change in internal energy of gases
W = Work done on gases = - 155 KJ
For an isobaric process (i.e constant pressure) we know that:
ΔQ = change in enthalpy = ΔH
ΔQ = 215 KJ
Therefore, using values in the equation, we get:
ΔU = 215 KJ - (-155 KJ)
<u>ΔU = 370 KJ</u>
b)
Since, the enthalpy of products is greater than the reactants. Therefore, this is an <u>endothermic reaction</u>.
Answer: 2.22 litres
Explanation:
Given that,
Original pressure of gas (P1) = 200.0 kPa
[Since final pressure is given in atmosphere, Convert 200.0 kPa to atmosphere
If 101.325 kPa = 1 atm
200.0 kPa = 200.0/101.325
= 1.9738 atm]
Original volume of oxygen O2 (V1) = 25.5L
New pressure of gas (P2) = 11.2 atm
New volume of gas (V2) = ?
Since pressure and volume are given while temperature is held constant, apply the formula for Boyle's law
P1V1 = P2V2
0.9738 atm x 25.5L = 11.2 atm x V2
24.8319 atm•L = 11.2 atm•V2
Divide both sides by 11.2 atm to get V2
24.8319 atm•L/11.2 atm = 11.2 atm•V2/11.2 atm
2.217 L = V2
[Round 2.217L to the nearest hundredth as 2.22L]
Thus, the new volume of the gas at 11.2 atm of pressure is 2.22 litres
Answer:
m = 17
Explanation:
From the question we were given that
Triangle WZY is bisected by ZX; ZW = ZY
∠YXZ = (6m – 12)°
Based on the characteristics of the triangle, we see that triangle WYZ is an isosceles triangle (that is, triangle WXZ is equal to triangle YXZ)
<YXZ = <WXZ = 90°
Using ∠YXZ = (6m – 12)°
We have:
(6m – 12)° = 90°
6m = 90 + 12 ⇒ 6m = 102
m = 102 ÷ 6 = 17
m = <u>17</u>
<u>We therefore see that m is equal to 17</u>