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Answer: The missing coefficient is 2.
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
As in the products, there are 2 atoms of sodium, thus there will be 2 atoms of of sodium in the reactant as well. This will balance the number of hydrogen and oxygen atoms as well.
Thus the missing coefficient is 2.
The question is incomplete, here is the complete question.
If we start with 1.000 g of strontium-90, 0.805 g will remain after 9.00 yr. This means that the half-life of strontium-90 is ________ yr.
a. 28.8 b. 30.9 c. 35.4 d. 32.2
Answer : The half-life of strontium-90 is 28.8 years.
Explanation :
This is a type of radioactive decay and all radioactive decays follow first order kinetics.
First we have to calculate the rate constant.
Expression for rate law for first order kinetics is given by :
where,
k = rate constant
t = time taken for decay process = 9.00 year
a = initial amount or moles of the reactant = 1.000 g
a - x = amount or moles left after decay process = 0.805 g
Putting values in above equation, we get:
To calculate the half-life, we use the formula :
Therefore, the half-life of strontium-90 is 28.8 years.