(DrBob222 please help me)
A sample of 1.97 grams of Z is dissolved into
500 grams of water which is in a styrofoam
coffee cup. The temperature is monitored and
is found to rise from 25.015◦C to 25.484◦C.
What is ∆Hsolution for substance Z? Assume
no heat is lost/gained by the cup itself. The
specific heat of water is 4.184 J/g·
◦C and the
molecular weight of Z is 141 g/mol.
Answer in units of kJ/mol of Z.
PLEASE DO NOT ROUND OR USE SIG FIGS
The dissolution of X is exothermic since T increased. What was q?
q = mass H2O x specific heat H2O x (Tfinal-Tinital)
Then q = delta H and that is negative.
That is delta H/1.97 g and you convert that to mols by
(-dH/1.97g) x 141 g/mol = -dH/mol. Post your work if you get stuck.
To calculate the enthalpy change (∆Hsolution) for the dissolution of substance Z, we need to use the equation:
∆Hsolution = q / n,
where q is the heat absorbed or released during the process, and n is the number of moles of substance Z.
First, we need to calculate the heat absorbed or released (q) using the equation:
q = m × C × ∆T,
where m is the mass of water, C is the specific heat of water, and ∆T is the change in temperature.
Given:
- Mass of water (m) = 500 g
- Specific heat of water (C) = 4.184 J/g·°C
- Change in temperature (∆T) = 25.484°C - 25.015°C = 0.469°C
Substituting these values, we get:
q = (500 g) × (4.184 J/g·°C) × (0.469°C)
= 982.536 J
Next, we need to calculate the number of moles (n) of substance Z using its mass and molar mass.
Given:
- Mass of Z = 1.97 g
- Molar mass of Z = 141 g/mol
Substituting these values, we get:
n = (1.97 g) / (141 g/mol)
= 0.0139 mol
Finally, we can calculate ∆Hsolution:
∆Hsolution = (982.536 J) / (0.0139 mol)
= 70622.754 J/mol
Converting from joules (J) to kilojoules (kJ):
∆Hsolution = 70.622754 kJ/mol (Answer)
Thus, the enthalpy change (∆Hsolution) for substance Z is 70.622754 kJ/mol.
To calculate ∆Hsolution for substance Z, you can follow these steps:
1. Calculate the heat absorbed by the water using the equation:
q = mc∆T
where q is the heat absorbed, m is the mass of water, c is the specific heat of water, and ∆T is the change in temperature of the water.
q = (500 g)(4.184 J/g·°C)(25.484 - 25.015 °C)
2. Convert the heat absorbed to kilojoules by dividing the value by 1000:
q = ((500 g)(4.184 J/g·°C)(25.484 - 25.015 °C)) / 1000
3. Calculate the moles of Z using the molecular weight and mass of Z:
moles of Z = mass of Z / molecular weight of Z
moles of Z = 1.97 g / 141 g/mol
4. Calculate ∆Hsolution:
∆Hsolution = q / moles of Z
Now you can substitute the values into the equation and calculate ∆Hsolution for substance Z.