Question

Chemistry help

Answer 1

Question 3.

Answer:

They are equal in magnitude but opposite in sign.

Explanation:

Fusion is another word for melting 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)

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Question 4.

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)

Calculate q₁

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 = -5020 J

Calculate q₂

ΔH(cryst) = -334 J·g⁻¹

q₂ = 40.0 × (-334)

q₂ = -13 360 J

Calculate the total heat

q = -5 020 – 13 360

q = - 18 400 J

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

18 400 J.