chem questions

asked by @maggieg11 • over 1 year ago • Chemistry • 5 pts

Calorimetry challenge: How much heat is required to raise the temperature of 2.50 kg of iron from 20oC to 1700oC?

For iron: MP = 1535oC; ∆Hºfus = 247 J/g ; csolid = 0.449 J/gºC; cliquid = 0.824 J/gºC

I got 1.85 x 10^5. Could you check this?

Also....

You are asked to prepare a temperature bath that freezes at -12.5ºC using only water (Kf = 1.86 ºC/molal) and ammonium sulfate. How many grams of ammonium sulfate would you need in order to prepare this bath if you start with 500 g of water?

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1 answer

Hey there! So for this first question, we need a couple of extra steps in order to achieve the final answer. Notice that Iron has a melting point at 1535 C. As iron melts, its specific heat capacity changes. That means that we have to use different energies for each. Q1 will represent the energy from the initial 20 C to the melting point at 1535 C.

Q2 is found by looking at the fusion at the melting point. That energy is also essential, so we find it by using the equation. Q3 is then found by looking at the temperature from the melting point at 1535 C to the final temperature at 1700 C.

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For the second question, it is a simple freezing point depression calculation. You know all of the values here except for the moles of Ammonium sulfate. So that is what you are solving for. Solve for the moles of Ammonium sulfate and you will be able to solve for the missing grams of Ammonium sulfate. Hope this helps!

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answered by @sabrina • over 1 year ago