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Question

For the reaction A $\rightarrow$ products. 

The concentration of A at 10 minutes is ________ $\times10^{-3}$ mol $L^{-1}$ (nearest integer). 
The reaction was started with 2.5 mol $L^{-1}$ of A.

To find the concentration of A at 10 minutes, we first need to understand the given details about the reaction. The graph relates the half-life (\(t_{1/2}\)) to the initial concentration \([A]_0\) with a slope of 76.92.

Assuming a first-order reaction, the half-life \(t_{1/2}\) is independent of the initial concentration and can be expressed as:

\(t_{1/2} = \frac{0.693}{k}\)

For a zero-order reaction, the formula is:

\(t_{1/2} = \frac{[A]_0}{2k}\)

Given the linear relationship and the slope, we interpret this as a zero-order reaction. The slope \(76.92\) then relates to \(\frac{1}{2k}\).

Calculate the rate constant \(k\):

\[k = \frac{1}{2\times76.92} \approx 0.00650\, \text{min}^{-1}\]

For a zero-order reaction, the concentration at time \(t\) is:

\[[A] = [A]_0 - kt\]

Insert given values:

\[[A] = 2.5 - 0.00650 \times 10 = 2.5 - 0.065 = 2.435\, \text{mol } L^{-1}\]

Convert to the required unit:

\[2.435 \, \text{mol } L^{-1} = 2435 \times 10^{-3} \, \text{mol } L^{-1}\]

The concentration of A at 10 minutes is 2435 × 10-3 mol L-1, which falls within the expected range of 2435,2435.

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Important Questions from Physical Chemistry

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    Consider the above reaction, what mass of $CaCl_2$ will be formed if 250 mL of 0.76 M HCl reacts with 1000 g of $CaCO_3$ ? 
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  5. If equal volumes of $AB_2$ and $XY$ (both are salts) aqueous solutions are mixed, which of the following combination will give a precipitate of $AY_2$ at 300 K ? 
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