What composes a element
1 answer:
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Answer:
the enthalpy change for this reaction is -57.7 kJ/mol
Explanation:
Given:
HB₂O₃ = -1272.8 kJ/mol
HCOCl₂ = -218.8 kJ/mol
HBCl₃ = -403.8 kJ/mol
HCO₂ = -393.5 kJ/mol
Those are all standard enthalpies
Question: Calculate the enthalpy change for this reaction, ΔHreaction = ?
The enthalpy of the reaction is calculated using the standard enthalpies of formation of both products and reagents. To understand better, the reaction is as follows
B₂O₃ + 3COCl₂ → 2BCl₃ + 3CO₂
Where the compounds on the left are the reactants and the compounds on the right are the products
ΔHreaction = ∑ΔHproducts - ∑ΔHreactants
Please be careful with the signs.
Answer:
Explanation:
Let A₀ = the original amount of ⁵⁵Co .
The amount remaining after one half-life is ½A₀.
After two half-lives, the amount remaining is ½ ×½A₀ = (½)²A₀.
After three half-lives, the amount remaining is ½ ×(½)²A₀ = (½)³A₀.
The general formula for the amount remaining is:
A =A₀(½)ⁿ
where n is the number of half-lives
n = t/t_½
Data:
A = 1.90 ng
t = 45 h
t_½ = 18.0 h
Calculation:
(a) Calculate n
n = 45/18.0 = 2.5
(b) Calculate A
1.90 = A₀ × (½)^2.5
1.90 = A₀ × 0.178
A₀ = 1.90/0.178 = 10.7 ng
The original mass of ⁵⁵Co was .