Question

20 POINTS 2 QUESTIONS CAN YOU ANSWER THEM ???
1 Which of the following reactions is a synthesis reaction?
N2 + 3H2 → 2NH3
MgI2 + Br2 → MgBr2 + I2
KClO3 → KCl + O2
HCl + NaOH → NaCl + H2O
2 Suppose that the half-life of an element is 1000 years. How many half-lives will it take before one-eighth of the original sample remains?
8
125
12.5
3

Answer 1

Answer 1 : The synthesis reaction is, $N_2+3H_2\rightarrow 2NH_3$

Explanation :

Synthesis reaction : It is a type of reaction in which the reactants present in elemental state react to give a single product.

(1) $N_2+3H_2\rightarrow 2NH_3$

This is a synthesis reaction.

(2) $MgI_2+Br_2\rightarrow MgBr_2+I2$

This is a single displacement reaction in which the most reactive element displaces the least reactive element.

(3) $KClO_3\rightarrow KCl+O_2$

This is a decomposition reaction in which larger reactant decomposes to give two or more products.

(4) $HCl+NaOH\rightarrow NaCl+H_2O$

This is a neutralization reaction in which an acid and a base react to give a salt and water as a product.

Answer 2 : The number of half-lives it take will be, 3

Formula used :

$a=\frac{a_o}{2^n}$

where,

a = amount of reactant left after n-half lives = $\frac{1}{8}a_o$

$a_o$ = Initial amount of the reactant

n = number of half lives

Putting values in above equation, we get:

$\frac{1}{8}a_o=\frac{a_o}{2^n}$

$2^n=8=2^3$

n = 3

Therefore, the number of half-lives it take will be, 3