Answer:
Explanation:
We are asked to convert an amount in grams to moles. To do this, we use the molar mass. This is the number of grams in one mole of a substance. It is the same value numerically as the atomic mass on the Periodic Table, however the units are grams per mole, not atomic mass units.
Look up the molar masses for the individual elements.
- Sodium (Na): 22.9897693 g/mol
- Oxygen (O): 15.999 g/mol
Look back at the formula: Na₂O. Notice there is a subscript of 2 after sodium. This means there are 2 atoms of sodium in every molecule, so we have to multiply sodium's molar mass by 2 before adding oxygen's.
- Na₂O: 2(22.9897693 g/mol)+ 15.999 g/mol = 61.9785386 g/mol
Set up a ratio using the molar mass.
Multiply by the given number of grams.
Flip the ratio so the grams of sodium oxide can cancel each other out.
The original measurement of grams given has 3 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place.
The 4 in the thousandth place tells us to leave the 8.
There are <u>2.48 moles of sodium oxide</u> in 154 grams, so choice A is correct.
The bad smelling element is Sulfur, which smells like rotting eggs.
Extrusive Rocks. Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks. They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow.
Answer:
(a) 0.699 kJ/K
(b) -0.671 kJ/K
(c) 0.028 kJ/K
Explanation:
The Refrigerant-134a flows into the evaporator as a saturated liquid-vapor mixture and flows out as a saturated vapor at a saturation pressure of 160 kPa and temperature of -15.64°C (estimated from the Saturated Refrigerant-134a Temperature Table).
(a) The entropy change of the refrigerant (ΔS
) = Q/T
Q = 180 kJ
T = -15.64 + 273.15 = 257.51 K
ΔS = Q/T = 180/257.51 = 0.699 kJ/K
(b) The entropy change (ΔS
) of the cooled space (ΔS) = -Q/T
Q = -180 kJ
T = -5 + 273.15 = 268.15 K
ΔS = Q/T = -180/268.15 = -0.671 kJ/K
(c) The total entropy change for this process (ΔS
) = ΔS + ΔS = 0.699 - 0.671 = 0.028 kJ/K
I will show you with detailed work for NaCl, but follow the same procedure for the rest of the compounds.
Molar Mass - Find the molar mass of the Na and the Cl and add them together
Na - 23
Cl - 35.5
Add those numbers together 23 + 35.5 = 58.5 g/mol
Moles in 1 tsp:
The mass measured in 1tsp of NaCl was 18 g. To calculate the amount of moles you take the mass measured and divide it by the molecular weight.
18/58.5 = 0.3077 mol
Moles of each element:
To find the moles each element in the compound you multiply the moles of 1 tsp by the number of atoms of the element in the compound
Na - 1 in NaCl
Cl - 1 in Na Cl
so take 0.3077 * 1 = 0.3077 moles Na (and Cl in this case)
Atoms of each:
take the number of moles calculated and multiply that by Avogadro's number(6.023x10^23) for the number of molecules
So for both Na and Cl:
0.3077 * 6.023x10^23 = 1.853x10^23 atoms for both Na and Cl
