Calculating Molar Heat of Reaction for Ca + HCl

[haydn]

Homework Statement

When 0.612 g of Ca metal is added to 200.0 mL of 0.500 M HCl(aq), a temperature increase of 100C is observed.
Assume the solution's final volume is 200.0 mL, the density is 1.00 g/mL, and the heat capacity is 4.184 J/gC.
(Note: Pay attention to significant figures. Do not round until the final answer.)
The molar heat of reaction, H rxn, for the reaction of

Ca_(s) + 2H⁺_(aq) => Ca²⁺_(aq) + H_{2 (g)}

Homework Equations

Q=mc$$\Delta$$T

The Attempt at a Solution

All I know is that mc$$\Delta$$T is used... Our professor hasn't taught us how to do this yet so that's about all I know. Would I divide Q by the number of moles formed?

 

[nate808]

Hi there,

Thank you for your post. It seems like you are trying to determine the molar heat of reaction for the reaction between calcium and hydrochloric acid. First, let's review the equation for calculating heat:

Q = mcΔT

Where:
Q = heat energy (in joules)
m = mass (in grams)
c = specific heat capacity (in J/g°C)
ΔT = change in temperature (in °C)

In this case, we know the mass of calcium added (0.612 g), the specific heat capacity (4.184 J/g°C), and the change in temperature (100°C). However, we need to determine the heat energy (Q) in order to calculate the molar heat of reaction.

To determine Q, we can use the following equation:

Q = (m)(c)(ΔT)

Substituting in the values we know, we get:

Q = (0.612 g)(4.184 J/g°C)(100°C)
Q = 256.4688 J

Now, to calculate the molar heat of reaction, we need to use the following equation:

H rxn = Q/n

Where:
H rxn = molar heat of reaction (in J/mol)
Q = heat energy (in joules)
n = moles of the limiting reactant (in mol)

In this case, calcium is the limiting reactant, so we need to determine the moles of calcium present in the reaction. To do this, we can use the following equation:

n = m/M

Where:
n = moles (in mol)
m = mass (in grams)
M = molar mass (in g/mol)

Substituting in the values we know, we get:

n = (0.612 g)/(40.078 g/mol)
n = 0.01525 mol

Now, we can plug in our values into the equation for molar heat of reaction:

H rxn = (256.4688 J)/(0.01525 mol)
H rxn = 16822.557 J/mol

Finally, we can round this to the appropriate number of significant figures, which would be 17000 J/mol.

I hope this helps and good luck with your studies!

 

[Blueshift5]

I would first gather all the necessary information and data provided in the problem. I would also review any relevant equations and concepts related to molar heat of reaction.

Next, I would calculate the amount of heat released or absorbed (Q) using the given mass, volume, and temperature change. This can be done using the equation Q=mcΔT, where m is the mass, c is the heat capacity, and ΔT is the change in temperature.

Then, I would use the molar ratio between Ca and H2 in the balanced chemical equation to determine the moles of Ca reacted. From there, I would calculate the molar heat of reaction (H rxn) by dividing Q by the moles of Ca reacted.

Finally, I would round the answer to the appropriate number of significant figures, keeping in mind the given values and their corresponding significant figures.

It is important to note that this is just one possible approach to solving this problem and there may be other methods or variations depending on the specific circumstances or instructions given by the professor. It is always best to consult with your professor or refer to your class notes and resources for guidance on how to approach and solve problems like this.