Answer:
- <em>The substance that cannot be broken down by a chemical change is </em><u>tungsten (option C)</u>
Explanation:
Chemical compounds are pure <em>substances</em> constituted by two or more different elements. They have fixed composition and have their unique chemical properties, different from their individual components (elements) and from other compounds.
Thus chemical compounds can<em> be broken down by a chemical change</em> into their individual atoms or other simpler compounds.
The substances indicated by the choices <em>A) methane, B) propanal, and D) water</em>, are chemical compounds with chemical formulae CH₄, C₃H₆O, and H₂O, respectively, so they<em> can be broken down into their consitutents by a chemical change</em>.
On the other hand, <em>tungsten</em> is one of the 118 known elements. Its atomic number is 74, and its chemical symbol is W.
Then, being tungsten an element, which means that all the atoms present in a pure sample have the same number of protons and electrons, it <em>cannot be broken down by a chemical change</em>. The only way to split an atom of tungsten is by a nuclear reaction.
Answer:
D. bromine
Explanation:
Highest electronegativity in the period has element closest to the *A group
K Ca Cu Br
Ernest Rutherford was a famous British physicist who lived and worked in the 19th and the first half of the 20th century. He is now considered to be the father of nuclear physics, given that he was the one responsible for figuring out about the nuclear structure of an atom (proton, electron, neutron) and about the nuclear processes in general. The element rutherfordium (Rf) is named after this scientist. When it comes to his personal life, his parents are both British, however, Ernest was born in New Zealand because his mom and dad before he was born. He worked as a professor in several universities, and was even knighted in 1914. He is a Nobel prize winner, which he won for Chemistry in 1908.
Answer:
The correct order of increasing reactivity toward nucleophilic acyl substitution is E < D < C < A < F < B.
Explanation:
The stability of the leaving group best determines the manner of reactivity of carboxylates to nucleophilic substitution after the substitution of the nucleophile to the leaving group. The leaving group should, therefore, be protonated with hydrogen ion in the solution to form a stable molecule. From the given list: The leaving group for A, Ethyl thioacetate will be ethanethiol. For B, Acetyl chloride will be Hydrochloric acid. For C, Sodium acetate will be Sodium Hydroxide. For D, Ethyl acetate will be Ethanol. For E, Acetamide will be Ammonia, and for F, Acetic anhydride will be Ethanoic acid. The reactivity of the substitution reaction is dependent on the stability of these leaving groups. The stability of these leaving groups depends on their pKa, and the more the pKa, the lesser the acidity of the leaving group, and the lower the reactivity. Therefore, considering their pKa: A is 8.5, B is -7, C is 13.8, D is 15.9, E is 36, and F is 4.8. When we rearrange this pKa in descending order, we have E, D. C, A, F, B. Which is also the increased reactivity of the nucleophilic acyl substitution.