Here are the answers to your questions:
Question 15
The balanced equation is:
\[ 3A_2 + 2B \rightarrow 2A_3B \]
- Molar mass of A = 4 g/mol.
- The molar mass of B = 16 g/mol.
- Initial mass of element A = 48 g.
To find out how many moles of A are present:
- \( \text{Moles of A} = \frac{\text{mass}}{\text{molar mass}} = \frac{48 , \text{g}}{4 , \text{g/mol}} = 12 , \text{mol} \)
According to the balanced equation, 3 moles of \( A_2 \) react with 2 moles of B. This means:
- For every 3 moles of \( A_2 \), 2 moles of B are required.
From the equation, moles of B needed can be calculated:
\[ \text{Moles of B needed} = \frac{2}{3} \times 12 , \text{mol} = 8 , \text{mol} \]
Now, convert moles of B to grams:
- \( \text{Mass of B} = \text{moles} \times \text{molar mass} = 8 , \text{mol} \times 16 , \text{g/mol} = 128 , \text{g} \)
Final Answer: 128g
Question 16
To calculate the number of molecules of carbon dioxide (CO₂) in a 17-gram sample:
-
Molar mass of CO₂:
- C: 12.01 g/mol
- O₂: 2 × 16.00 g/mol = 32.00 g/mol
- \[ \text{Molar mass of CO₂} = 12.01 + 32.00 = 44.01 , \text{g/mol} \]
-
Calculate moles of CO₂ in 17 g:
\[ \text{Moles of CO₂} = \frac{17 , \text{g}}{44.01 , \text{g/mol}} \approx 0.386 , \text{mol} \] -
Convert moles to molecules using Avogadro's number (\(6.022 \times 10^{23} , \text{molecules/mol}\)):
\[ \text{Number of molecules} = 0.386 , \text{mol} \times 6.022 \times 10^{23} , \text{molecules/mol} \approx 2.32 \times 10^{23} \]
Final Answer: 2.326×10²³
Question 17
Correct statement about protons and neutrons in a nuclear change:
Final Answer: The total atomic mass before and after the change remains the same, but the total charge is different.
Question 18
Accurate description of nuclear fission:
Final Answer: Fission is a process in which a large nucleus is split into smaller nuclei.
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