12.5% of strontium-90 would remain in a sample after three half-lives have passed. Half-life automatically means 50% of the original amount would remain.
Answer:
5.95g
Explanation:
1 
= 1000 mL
∴ 100 mL = 100 ÷ 1000 = 0.1
Volume = <u>0.1 </u><u />
Concentration = <u>0.5 M</u>
Concentration = 
0.5 = 
No. of moles = 0.5 x 0.1 = <u>0.05 moles</u>
No. of moles = 
Mass in 1 mole of KBr = 39 + 80 = 119g (39 is the mass of potassium and 80 is the mass of bromine)
0.05 = 
x = 119 × 0.05 = 5.95g
The most stable conformation of
trans-1-tert-butyl-2-methylcyclohexane is the one in which both the
tert-butyl group and the methyl group are located near the equatorial position.
Trans conformation are usually stable at the equatorial position to avoid the
bulkyl group ( the tert-butyl group and methyl group) be together to reduce the
so called Steric hindrance.
Answer:
Explanation:
This question is incomplete. However, let's understand what a single displacement reaction is and what occurs during such reactions.
A single displacement reaction is a reaction in which a more reactive element displaces/replaces a less reactive element in a compound. The reactions below depict a single displacement reaction.
A + BC ⇒ AC + B
2Al + Fe₂O₃ ⇒ Al₂O₃ + 2Fe
During chemical reactions, heat is either absorbed from the environment (endothermic reaction) or given off into the environment (exothermic reaction). <u>During bond formation (in a reaction), heat is released into the environment (exothermic) while when bonds are broken, heat is absorbed from the environment (endothermic).</u>
During single displacement reaction, heat is given off, hence single displacement reaction is an exothermic reaction because it involves the formation of a bond (for the compound formed in the product).
Please note that <u>it can be argued that bonds were also broken in the reactants before new ones are formed in the products, however the bonds broken in the reactant do not require much heat from the environment because the more reactive element ordinarily has a higher activity than the displaced element thus, the entire reaction produces heat (exothermic) when the new bond is being formed</u>.
What is usually observed during a single displacement reaction is the release of heat and this shows the reaction is an exothermic reaction.
Beryllium does not react directly with hydrogen unlike other alkaline earth metals to form ionic hydride. This is because the oxidation potential of beryllium is very low and thus it does not donate its electrons easily to hydrogen.
