If Enthalpy is positive, the reaction is endothermic.
If Enthalpy is negative, the reaction is exothermic.
Answer: C) Roman numeral following the name.
Explanation: If we want to name an ionic compound like NaCl then we can easily write its name. Na is sodium and Cl is chlorine. First we write the name of the metal ion and then the name of the anion it has. Here we have mono atomic ion and for these we use the suffix -ide. So, the name will be sodium chloride.
Now, if we have something like 
and we write the name as Iron chloride, then it will not be correct since Fe is a transition metal and it shows +2 and +3 oxidation states. So, to overcome this difficulty, a roman numeral is used for the oxidation state of the metal ion. The name of above compound will be Iron(III)chloride. Similarly, if we have 
then its name will be written as Iron(II)chloride.
In both the above names, the roman numerals (III) and (II) are indicating numerical value of the charge of the metal ion. So, the correct choice is C) Roman numerals following the name.
when naming a transition metal ion that can have more than one common ionic charge, the numerical value of the charge can be indicated by a Roman numeral following the name.
Answer:
Because it can cause health problems or injuries to our sense organs.
Explanation:
Chemicals in the laboratory are made up of different constituents, which may be dangerous or injurious to health. This is the reason why safety measures or precautions have to be taken when working in the laboratory. One of those safety measures is that "one should never use taste, touch, or smell to identify an unknown chemical".
This is so because a chemical that is unknown amounts to the fact that what such chemical contains is unknown, hence, the chemical might have the ability to cause harm or injuries to the sense organ. For example, a conc. acid that is tasted will burn the tongue etc.
7.5 mol of hydrogen would be needed to consume the available nitrogen.
Explanation:
When hydrogen reacts with nitrogen, ammonia is formed as shown below;
3H₂ (g) + N₂ (g) → 2NH₃ (g)
As seen from the equation, every 3 moles of H₂ react with a mole of N₂ to form 2 moles of NH₃.
The limiting factor in a chemical reaction is the reactant that gets depleted first.
Because the molar mass of nitrogen gas is approximately 28g/mol, 70g of nitrogen gas would be 2.5 moles.
The reaction ratio of nitrogen to hydrogen in the reaction is 1 : 3. The reaction would require 2.5 * 3 (7.5) moles of hydrogen for a complete reaction.
However since there are only 7g on hydrogen, (Remember 1 mole of H₂ is approximately 2g), the available moles of H₂ is 7 / 2 = 3.5
3.5 moles fall short of the 7.5 moles of H₂ required for a complete reaction. H₂ gets depleted first before N₂. The reaction would require 4 more moles of H₂.
