Answer:
At earlier times elements were arrangrd on the basis of their atomic masses to study their properties easily but there were various problems like isotopes needs different position in perodic table.
After discovery of atomic number modern periodic table was created on the basis of atomic number (number of proton) that is unique for each element and varies regularly. So study of a group of elements is much easier than each element seperately that is why modern periodic table was formed.
Explanation:
Balanced chemical equation:
* moles of oxygen
4 Al + 3 O2 = 2 Al2O3
4 moles Al -------------- 3 moles O2
9.30 moles Al ---------- moles O2
moles O2 = 9.30 * 3 / 4
moles O2 = 27.9 / 4 => 6.975 moles of O2
Therefore:
Molar mass O2 = 31.9988 g/mol
n = m / mm
6.975 = m / 31.9988
m = 6.975 * 31.9988
m = 223.19 of O2
What we're looking for here is the gas sample's molar mass given its mass, pressure, volume, and temperature. Recalling the gas law, we have

or

where R is <span>0.08206 L atm / mol K, P is the given pressure, T is the temperature, and V is the volume.
Before applying the values given, it is important to make sure that they are to be converted to have consistent units with that of R.
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Thus, we have
P = 736/ 729 = 0.968 atm
T = 28 + 273.15 = 301.15 K
V = 250/1000 = 0.250 L
Now, applying these converted values into the gas law, we have


Given that the mass of the sample is 0.430 g, we have

Thus, the gas sample has a molar mass of 43.9 g/mol.
Answer:
The statement that is not true is: 'Temperature does not affect the reaction rate'.
Explanation:
a) Temperature can change a reaction rate. <u> This is true</u>
Increasing the temperature increases the reaction rates because of the disproportionately large increase in the number of high energy collisions. It is only these collisions (possessing at least the activation energy for the reaction) which result in a reaction.
For example, the time taken to melt a metal will be much higher at a lower temperature but it will decrease as soon as we increase the temperature
b) The amount of reactants can increase the reaction rate.<u> This is true</u>
A higher concentration of reactants leads to more effective collisions per unit time, which leads to an increased reaction rate.
c) Temperature can decrease the reaction rate. <u>This is true </u>
Decreasing the temperature decreases the reaction rates because of the decrease in the number of high energy collisions. It will result in a slower reaction.
d) Temperature does not affect the reaction rate. <u>This is not true. </u>
The reaction rate is temperature dependent. The reaction rate increases with higher temperature and decreases with lower temperature.