Answer:
- <em><u>Mendeleev produced the first orderly arrangement of known elements.</u></em>
- <em><u>Mendeleev used patterns to predict undiscovered elements.</u></em>
Explanation:
- <u>Mendeleev produced the first orderly arrangement of known elements and used patterns to predict the undiscovered elements.</u>
Those two statments are true.
For the time being there were some 62 known elements. Before Medeleev some schemes to order part of the elements were proposed, but Medeleev showed the relationship between the atomic mass and the properties of the elements (supports second choice). This arrangement is known as the periodic table.
More importantly, Mendeleev predicted correctly the existance and properties of unknown elements, which is his major contribution: he left blanket spaces which where gradually filled when new elements where discovered (this supports the fourth choice).
The first modern chemistry book was written by Antoine Lavoisier (this discards first option).
Mendeleev ordered the elements by increasing mass number (this discards third choice), which was corrected later by the scientist Henry Moseley, who ordered the elements by increasing atomic number (number of protons).
Isotopes were not known by Mendeleev times, so this discards the last option.
Answer:
ΔE = 73 J
Explanation:
By the first law of thermodynamics, the energy in the system must conserved:
ΔE = Q - W
Where ΔE is the internal energy, Q is the heat flow (positive if it's absorbed by the system, and negative if the system loses heat), and W is the work (positive if the system is expanding, and negative if the system is compressing).
So, Q = + 551 J, and W = + 478 J
ΔE = 551 - 478
ΔE = 73 J
The name of the covalent compound CCl4 is 'Carbon tetrachloride'.
Hope this helps!
Answer:
1. filtration and evaporation
2. i) water is added to the sand and salt mixture
ii) then the mixture is filtrated and so the sand and the salt water was seperated
iii) the salt water is heated with the help of burner until the water gets evaporated
iv) after the water gets evaporated, the salt is remained in the container
3. observation:
- on adding water to the mixture, the salt is completely dissolved in the water
- when filtrated the sand is seperated from the salt water
- now the salt water when heated with the burner until the evaporation, the water is evaporated
- the salt is precipitated and remained in the container
4. cautions:
- while using the burner, we should be cautious with fire
- the container that is heated should be holded with the help of a cloth to avoid heat
There would be 2 which would be on the oxygen
