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Multiple Choice
A 100 mL sample of 0.3 M NaOH is mixed with a 100 mL sample of 0.3 M HCl in a coffee cup calorimeter. If both solutions were initially at 35°C and the temperature of the resulting solution was recorded as 37°C, determine ΔH_rxn (in units of kJ/mol NaOH) for the reaction.
A
-13.9 kJ/mol
B
-25.0 kJ/mol
C
-75.0 kJ/mol
D
-55.8 kJ/mol
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검증된 단계별 안내
1
Identify the reaction: The reaction between NaOH and HCl is a neutralization reaction, represented by the equation: \( \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} \).
Calculate the total volume and concentration: Since both solutions are mixed, the total volume is 200 mL (100 mL NaOH + 100 mL HCl). The concentration of each reactant remains 0.3 M because they are mixed in equal volumes and concentrations.
Determine the moles of reactants: Use the formula \( \text{moles} = \text{concentration} \times \text{volume} \). For NaOH, \( \text{moles of NaOH} = 0.3 \text{ M} \times 0.1 \text{ L} = 0.03 \text{ moles} \). Similarly, calculate the moles of HCl.
Calculate the heat absorbed or released: Use the formula \( q = m \cdot c \cdot \Delta T \), where \( m \) is the mass of the solution (assuming density of water, 1 g/mL, so 200 g), \( c \) is the specific heat capacity of water (4.18 J/g°C), and \( \Delta T \) is the change in temperature (37°C - 35°C).
Determine \( \Delta H_{\text{rxn}} \): Convert the heat \( q \) from joules to kilojoules, then divide by the moles of NaOH to find \( \Delta H_{\text{rxn}} \) in kJ/mol. Remember to consider the sign of \( \Delta H \) based on whether the reaction is exothermic or endothermic.