Pure substances can or can not be chemically combined.
Pure substances can be either elements or compounds, but not mixture. Mixture are different substances mixing together without being chemically combined, such as air, which is a mixture of oxygen, carbon dioxide, water etc. Mixture can be separated by physical methods, like filtration or decantation.
Meanwhile, elements are the substances that cannot be further separated by any means. No matter physical or chemical methods. Examples of elements are oxygen, hydrogen, neon and all the other ones from the periodic table. Compounds are basically elements joining together, but they’re chemically combined which means their electrons (kind of subatomic particle) are either shared or given away. These elements can only be separated by chemical methods like electrolysis or heating.
Therefore, as long as the substance cannot be separated by physical methods, it can be considered as a pure substance. We can now conclude that pure substance can be (element) or can not be (compound) chemically combined.
Answer:
234.35 °C
Explanation:
Given data:
Volume of balloon = 125000 mL
Moles of oxygen = 3 mol
Pressure = 1 atm
Temperature = ?
Solution:
Formula:
PV = nRT
P = Pressure
V = volume
n = number of moles
R = ideal gas constant
T = temperature
Volume of balloon = 125000 mL × 1 L /1000 mL
Volume of balloon = 125 L
Now we will put the values:
Ideal gas constant = R = 0.0821 atm.L/mol.K
PV = nRT
T = PV/nR
T = 1 atm × 125 L/ 0.0821 atm.L/mol.K × 3 mol
T= 125 /0.2463 /K
T = 507.5 K
K to °C
507.5 K - 273.15 = 234.35 °C
Answer:
I think B..
Explanation:
It is the sharing of electrons from one atom to another .
Answer: Positive, positive
Explanation:
Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.
is positive when randomness increases and is negative when randomness decreases.
Exothermic reactions are defined as the reactions in which energy is released in the form of heat and 
for the reaction comes out to be negative.
Endothermic reactions are defined as the reactions in which energy is absorbed in the form of heat and for the reaction comes out to be positive.
For a cold pack, the energy has to be absorbed for the dissolution of ammonium nitrate in water so that the surroundings feel cold.Thus as energy is absorbed, for the reaction comes out to be positive.
The solid form of ammonium nitrate is getting converted to ions and thus entropy increases and thus for the reaction comes out to be positive.
Answer:
(a) 
(b) 
(c) 
Explanation:
Hello,
In this case, given the molality in mol/L, we can compute the required units of concentration assuming a 1-L solution of acetonitrile and lithium bromide that has 1.80 moles of lithium bromide:
(a) For the molality, we first compute the grams of lithium bromide in 1.80 moles by using its molar mass:
Next, we compute the mass of the solution:
Then, the mass of the solvent (acetonitrile) in kg:
Finally, the molality:
(b) For the mole fraction, we first compute the moles of solvent (acetonitrile):
Then, the mole fraction of lithium bromide:
(c) Finally, the mass percentage with the previously computed masses:
Regards.
