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ch4aika [34]
4 years ago
8

Chemistry help

Chemistry
1 answer:
Agata [3.3K]4 years ago
3 0

<em>Question 3. </em>

Answer:

They are equal in magnitude but opposite in sign.

Explanation:

Fusion is another word for <em>melting</em> and crystallization is another word for freezing.

They are opposite processes, so the heat you must add (positive sign) to melt a substance is equal to the heat released but with a negative sign.

ΔH(fus) = -ΔH(cryst)

===============

<em>Question 4. </em>

Answer:

18 400 J

Explanation:

There are two heat transfers in this question.

Total heat = heat to cool water + heat to freeze water

      q         =               q₁              +                q₂

      q         =            mCΔT          +        mΔH(freeze)

<em>Calculate q₁ </em>

m = 40.0 g

C = 4.184 J·K⁻¹g⁻¹

ΔT = T_f – T_i = 0 °C - 30 °C = -30 °C

q₁ = 40.0 × 4.184× (-30)

q₁ = <em>-5020 J </em>

<em>Calculate q₂ </em>

ΔH(cryst) = -334 J·g⁻¹

q₂ = 40.0 × (-334)

q₂ = <em>-13 360 J </em>

<em>Calculate the total heat </em>

q = -5 020 – 13 360

q = - 18 400 J

The negative sign shows that heat is removed, so you must remove

18 400 J.

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