Consider the following reaction: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
0.103 g of Zn is combined with enough HCl to make 50.0 mL of solution in a coffee-cup calorimeter. As all of the Zn reacts, the temperature of the solution increases from 22.5°C to 23.7°C. Find ΔHrxn (in kJ) for the overall reaction. Assume 1.0 g/mL is the density of the solution and 4.18 J/g°C is the specific heat capacity of the solution.
I know that the equation is ΔHrxn = -qsoln
and
-qsoln = msoln x Cs,soln x ΔT
is m moles or grams? how would you get moles?
Im confused on where to start
msoln is mass of the solution. At a density of 1.0 g/mL, then mass is 50 grams. Use that to determine the q. I think the problem lacks some clarity. dH for the REACTION, I think, is just that -q. You COULD say that dH rxn was -q/0.103 g; however, most problems ask for dH rxn in kJ/mol. So you use -q soln/mols Zn reacted and convert to kJ.
To solve this problem, we need to find the heat released or absorbed by the reaction (ΔHrxn) using the equation ΔHrxn = -qsoln.
We are given the mass of Zn (0.103 g) and the volume of the solution (50.0 mL). The density of the solution is given as 1.0 g/mL, which means the mass of the solution is equal to its volume.
To convert the volume of the solution to grams, we can use the density formula:
mass = volume x density
mass = 50.0 mL x 1.0 g/mL = 50.0 g
So, the mass of the solution is 50.0 g.
Next, we need to calculate the heat absorbed or released by the solution (qsoln). The equation for qsoln is:
qsoln = msoln x Cs,soln x ΔT
where msoln refers to the mass of the solution, Cs,soln is the specific heat capacity of the solution, and ΔT is the change in temperature.
In this case, msoln is 50.0 g, Cs,soln is 4.18 J/g°C (given), and ΔT is the change in temperature, which can be calculated as:
ΔT = final temperature - initial temperature
ΔT = 23.7°C - 22.5°C
ΔT = 1.2°C
Now we can substitute the values into the equation:
qsoln = 50.0 g x 4.18 J/g°C x 1.2°C
This will give us the value for qsoln in joules. However, we need to convert it to kilojoules (kJ). Since 1 kilojoule (kJ) is equal to 1000 joules (J), we divide the value of qsoln by 1000:
qsoln = (50.0 g x 4.18 J/g°C x 1.2°C) / 1000
qsoln = 2.502 kJ
Finally, we can find ΔHrxn using the equation ΔHrxn = -qsoln:
ΔHrxn = -2.502 kJ
Therefore, the ΔHrxn for the overall reaction is -2.502 kJ.