Questions: A student dissolves 13.3 g of lithium chloride (LiCl) in 250 g of water in a well-insulated open cup. She then observes the temperature of the water rise from 22.0°C to 32.8°C over the course of 6.5 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: LiCl(s) -> Li^(+)(aq) + Cl^(-)(aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the correct number of significant digits. Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction. Is this reaction exothermic, endothermic, or neither? - exothermic O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. square kJ Calculate the reaction enthalpy ΔH per mole of LiCl. square kJ/mol

A student dissolves 13.3 g of lithium chloride (LiCl) in 250 g of water in a well-insulated open cup. She then observes the temperature of the water rise from 22.0°C to 32.8°C over the course of 6.5 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: LiCl(s) -> Li^(+)(aq) + Cl^(-)(aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the correct number of significant digits. Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction. Is this reaction exothermic, endothermic, or neither? - exothermic O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. square kJ Calculate the reaction enthalpy ΔH per mole of LiCl. square kJ/mol
Transcript text: A student dissolves 13.3 g of lithium chloride (LiCl) in 250 g of water in a well-insulated open cup. She then observes the temperature of the water rise from 22.0°C to 32.8°C over the course of 6.5 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: \[ \mathrm{LiCl}(s) \rightarrow \mathrm{Li}^{+}(a q)+\mathrm{Cl}^{-}(a q) \] You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the correct number of significant digits. Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction. Is this reaction exothermic, endothermic, or neither? - exothermic O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. $\square \mathrm{kJ}$ Calculate the reaction enthalpy $\Delta H_{m \mathrm{mn}}$ per mole of LiCl. $\square \frac{\mathrm{kJ}}{\mathrm{mol}}$
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Solution

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Solution Steps

Step 1: Determine if the Reaction is Exothermic or Endothermic

The temperature of the water increased from \(22.0^{\circ} \mathrm{C}\) to \(32.8^{\circ} \mathrm{C}\). This indicates that the reaction released heat to the surroundings, causing the temperature to rise. Therefore, the reaction is exothermic.

Step 2: Calculate the Heat Released by the Reaction

To calculate the heat released, we use the formula: \[ q = m \cdot c \cdot \Delta T \] where:

  • \(m\) is the mass of the water (250 g),
  • \(c\) is the specific heat capacity of water (\(4.184 \, \mathrm{J/g \cdot ^\circ C}\)),
  • \(\Delta T\) is the change in temperature (\(32.8 - 22.0 = 10.8 \, ^\circ C\)).

Substituting the values: \[ q = 250 \, \mathrm{g} \times 4.184 \, \mathrm{J/g \cdot ^\circ C} \times 10.8 \, ^\circ C = 11300.8 \, \mathrm{J} \]

Convert joules to kilojoules: \[ q = 11.3008 \, \mathrm{kJ} \]

Step 3: Calculate the Reaction Enthalpy per Mole of LiCl

First, calculate the number of moles of LiCl: \[ \text{Molar mass of LiCl} = 6.94 \, (\text{Li}) + 35.45 \, (\text{Cl}) = 42.39 \, \mathrm{g/mol} \] \[ \text{Moles of LiCl} = \frac{13.3 \, \mathrm{g}}{42.39 \, \mathrm{g/mol}} = 0.3138 \, \mathrm{mol} \]

Now, calculate the reaction enthalpy \(\Delta H\) per mole of LiCl: \[ \Delta H = \frac{q}{\text{moles of LiCl}} = \frac{11.3008 \, \mathrm{kJ}}{0.3138 \, \mathrm{mol}} = 36.02 \, \mathrm{kJ/mol} \]

Final Answer

  • The reaction is \(\boxed{\text{exothermic}}\).
  • The heat released by the reaction is \(\boxed{11.30 \, \mathrm{kJ}}\).
  • The reaction enthalpy per mole of LiCl is \(\boxed{36.02 \, \mathrm{kJ/mol}}\).
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