The Chemistry Regents is one of the four science Regents exams. The other three are Earth Science, Living Environment, and Physics. You'll need to pass at least one of these four exams to graduate high school.
Answer:
Mendeleev had left the noble gases out of his periodic table.
Explanation:
Mendeleev's periodic table is pictured in the image attached to the question.
Mendeleev's table obviously lacked the noble gases. The reason for this grave omission is simple; the noble gases were not known as at the time when he formulated his periodic table. There weren't any known elements whose properties were similar to the properties of the noble gases. This would have lead him to suspect their existence.
Answer:
Explanation:
Given that:
The Half-life of 
= 
is less than that of 
Although we are not given any value about the present weight of .
So, consider the present weight in the percentage of to be y%
Then, the time elapsed to get the present weight of = 
Therefore;
here;
= Number of radioactive atoms relating to the weight of y of
Thus:
--- (1)
However, Suppose the time elapsed from the initial stage to arrive at the weight of the percentage of to be = 
Then:
---- (2)
here;
= Number of radioactive atoms of relating to 3.0 a/o weight
Now, equating equation (1) and (2) together, we have:
replacing the half-life of =
( since 
)
∴
The time elapsed signifies how long the isotopic abundance of 235U equal to 3.0 a/o
Thus, The time elapsed is
Answer:
Electron
Explanation:
The answer would be the electron because it is constantly moving so its location cannot be accurately determined
Answer:
ΔH° = -186.2 kJ
Explanation:
Hello,
This case in which the Hess method is applied to compute the required chemical reaction. Thus, we should arrange the given first two reactions as:
(1) it is changed as:
SnCl2(s) --> Sn(s) + Cl2(g)...... ΔH° = 325.1 kJ
That is why the enthalpy of reaction sign is inverted.
(2) remains the same:
Sn(s) + 2Cl2(g) --> SnCl4(l)......ΔH° = -511.3 kJ
Therefore, by adding them, we obtain the requested chemical reaction:
(3) SnCl2(s) + Cl2(g) --> SnCl4(l)
For which the enthalpy change is:
ΔH° = 325.1 kJ - 511.3 kJ
ΔH° = -186.2 kJ
Best regards.
