What is the molar heat of reaction?
When 0.732 g of Ca metal is added to 200.0 mL of 0.500 M HCl(aq), a temperature increase of 119C 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) + H2(g)
is ? kJ/mol
So, I believe i use the equation q=m*s*delta T
and i divide it by n (solute)?
I keep getting the wrong answer. Please help
Use the temperature rise, mass and specific heat of the final product to determine the heat release. Divide that by the number of moles of the reactant calcium. (I am assuming that Ca is the limiting reactant, and disappears; this should be checked)
btw, i meant to write 11.9C not 119.
i work it like this:
200ml(1g/ml)(4.184J/C)(11.9C)
then divide by (40.078g/mol/.732g)
i get the wrong answer though
Divide first by 0.732 to give H/gram, then multiply by 40.078 to obtain H/mol. That will give you the right answer.
i get 545 but i'm not getting the right answer
nvm its -545. not quite sure why its exothermic
oh and thank you guys
To determine the molar heat of reaction, you need to use the equation q = m * C * ΔT, where q is the heat absorbed or released during the reaction, m is the mass of the solution, C is the specific heat capacity of the solution, and ΔT is the change in temperature.
In this case, you have a solution of HCl and you are adding calcium (Ca) metal to it. The reaction produces calcium ions (Ca2+) and hydrogen gas (H2). The molar heat of reaction (Hrxn) represents the heat released or absorbed per mole of the reacted substance.
To solve the problem, you need to follow these steps:
1. Calculate the heat absorbed or released (q) by using the equation: q = m * C * ΔT.
- The mass (m) of the solution is determined by the density of the solution: m = density * volume.
- The specific heat capacity (C) is given as 4.184 J/g°C.
- The change in temperature (ΔT) is given as 119°C.
2. Determine the moles of calcium (Ca) used in the reaction.
- Use the given mass (0.732 g) and the molar mass of calcium (40.08 g/mol) to calculate the moles of Ca.
3. Use the balanced equation to determine the moles of hydrogen gas (H2) produced.
- From the balanced equation, the stoichiometry is 1:1 for Ca:H2.
4. Calculate the molar heat of reaction (Hrxn) by dividing the heat absorbed or released (q) by the moles of Ca or H2, depending on which value you get from the previous step.
- Convert the value to kJ/mol.
By following these steps, you should be able to calculate the molar heat of reaction (Hrxn) for the given reaction.