Zinc metal reacts with hydrochloric acid according to the following balanced equation.
Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)
When 0.114 g of Zn(s) is combined with enough HCl to make 51.1 mL of solution in a coffee-cup calorimeter, all of the zinc reacts, raising the temperature of the solution from 22.5 degrees Celsius to 24.7 degrees Celsius .
Find Delta Hrxn for this reaction as written. (Use 1.0 g/mL for the density of the solution and 4.18 J/g*C as the specific heat capacity.)
Delta Hrxn =.........KJ
q = mass x specific heat x delta T.
That gives you q for 0.114 g Zn which I call delta H rxn (as it was run).
You can do q/0.114 if you want delta H in joules/g and that x 65.39 if you want delta H in joules/mole.
34.98
To find the enthalpy change (ΔHrxn) for the reaction as written, we can use the equation:
ΔHrxn = q / moles of Zn
First, we need to find the heat released or absorbed by the reaction (q).
q = m × c × ΔT
Where:
m = mass of solution in grams
c = specific heat capacity of the solution (given as 4.18 J/g·°C)
ΔT = change in temperature (final temperature - initial temperature)
To find the mass of the solution, we'll use the density of the solution.
Density = mass / volume
mass = density × volume
Given:
Volume of solution (V) = 51.1 mL = 51.1 g (since 1 mL = 1 g for water-based solutions)
Density of solution = 1.0 g/mL
mass of solution = density × volume = 1.0 g/mL × 51.1 g = 51.1 g
Now, let's calculate the change in temperature (ΔT):
ΔT = final temperature - initial temperature
ΔT = 24.7 °C - 22.5 °C = 2.2 °C
Next, we need to calculate the moles of Zn used in the reaction. To do this, we'll use the molar mass of zinc (Zn).
Molar mass of Zn = 65.38 g/mol
moles of Zn = mass of Zn (g) / molar mass of Zn (g/mol)
moles of Zn = 0.114 g / 65.38 g/mol
Now, we can substitute all the values into the equation to find ΔHrxn:
ΔHrxn = q / moles of Zn
ΔHrxn = (m × c × ΔT) / moles of Zn
ΔHrxn = (51.1 g × 4.18 J/g·°C × 2.2 °C) / (0.114 g / 65.38 g/mol)
Calculating the above expression will give us the value of ΔHrxn in J/mol. To convert it to kJ, we divide by 1000:
ΔHrxn = (51.1 × 4.18 × 2.2) / (0.114 / 65.38) / 1000
After performing the calculation, ΔHrxn is approximately equal to -434.9 kJ/mol (rounded to three significant figures).
Therefore, ΔHrxn for this reaction as written is -434.9 kJ/mol.
To find the value of ΔHrxn (the enthalpy change) for the given reaction, we can use the equation:
ΔHrxn = q / n
where q is the heat absorbed or released by the reaction and n is the number of moles of the limiting reactant. In this case, zinc is the limiting reactant.
Now, let's break down the calculation step-by-step:
1. Calculate the amount of heat absorbed or released by the reaction (q):
q = m * c * ΔT
where m is the mass (in grams) of the solution, c is the specific heat capacity of the solution, and ΔT is the change in temperature.
Given:
- Mass of solution (m) = volume * density = 51.1 mL * 1.0 g/mL = 51.1 g
- Specific heat capacity (c) = 4.18 J/g∙°C
- Change in temperature (ΔT) = final temperature - initial temperature = 24.7°C - 22.5°C = 2.2°C
Plugging in these values:
q = 51.1 g * 4.18 J/g∙°C * 2.2°C = 479.5024 J
2. Calculate the number of moles of zinc (n):
Given:
- Mass of zinc used = 0.114 g
- Molar mass of zinc (Zn) = 65.38 g/mol
n = mass / molar mass = 0.114 g / 65.38 g/mol ≈ 0.001743 mol
3. Calculate ΔHrxn:
ΔHrxn = q / n = 479.5024 J / 0.001743 mol = 275,418.348 J/mol
Converting from joules to kilojoules:
ΔHrxn ≈ 275.418 kJ/mol
Therefore, the value of ΔHrxn for the reaction as written is approximately 275.418 kJ/mol.