18. have a nice day hope it helps.
B.
When the object has passed over the observer, the pressure disturbance waves (Mach waves) radiate toward the ground, causing a sonic boom. ... Then, just as the aircraft bursts through the sound barrier, the air is locally disturbed by the resulting shock wave and the condensation/vapor cloud disappears.
Each orbital must contain a single electron before any orbital contains two electrons.
Always convert to moles when comparing compounds.
Molar mass of a compound is the sum of it's atomic molar mass units.
Mg = 24.3 g/mol Mg
O2 = 16 + 16 = 32 g/mol O2
MgO = 24.3 + 16 = 40.3 g/mol MgO
Determine the moles of each reactant/product.
2.2 g Mg * (1 mol/24.3 g Mg) = 0.09 mol Mg
3.6 O2 * (1 mol/32 g O2) = 0.1125 mol O2
2.7 g MgO * (1 mol/40.3 g MgO) = 0.067 mol MgO
Check if there's a limiting reagent. For every 1 O2 we need 2 Mg
0.1125 mol O2 * 2 = 0.225 mol Mg needed.
So Mg is a limiting reagent. We have plenty of O2 which is typically the case when oxygen is a reactant.
Figure out how much product should form based on the moles of limiting reagent. For every 2 Mg 2 MgO are formed. So it's a 1:1 ratio.
0.09 mol Mg ---> 0.09 mol MgO
compare the expected 0.09 mol MgO to the actual 0.067 mol MgO obtained. Calculate the percent obtained.
(0.067 mol MgO obtained) / (0.09 mol MgO expected) * 100 = 74.44 % yield
The third one because temperature is being used, so a meter stick wouldn’t make sense. You aren’t measuring the length of anything physically. A stopwatch measures time, which is what they are showing in the chart, so the third one is the only one that makes sense.