The heat of fusion of crystalline polyethylene is approximately 7.7 kJ/mol, and the corresponding entropy change for melting is 19 J mol^-1 K^-1. Use these data to estimate the melting point of polyethylene.

Strategy Because ΔH and ΔS are both positive, we know that ΔG must be positive at low temperatures and negative at higher temperatures. The melting point marks the dividing line between low and high temperatures. So at the melting point itself, G must be equal to zero. We can therefore start with Equation 10.4 and set ΔG = 0. That leaves T as the only unknown, so we can solve for the desired melting point.

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ΔG = ΔΗ – ΤAS (10.4)