Nine Degrees Against One
Ana gives 1 kg of water and a 1 kg block of iron the same 4,200 joules of heat. The water warms by 1 °C, and the iron by about 9 °C.
Where does the energy go in the water, if not into its temperature?
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Science · Honors Biology
Chapter 1: Biochemistry
A weak bond, in enormous numbers.
Ana gives 1 kg of water and a 1 kg block of iron the same 4,200 joules of heat. The water warms by 1 °C, and the iron by about 9 °C.
Where does the energy go in the water, if not into its temperature?
Make your guess to turn the page.
Still to come: 11 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students picture hydrogen bonds as weak covalent bonds, a permanent net. The book compares their strength with the O–H bond, then runs a heating curve whose two plateaus, 8 and 56 units wide, come from breaking vast numbers of transient bonds. Ask: if hydrogen bonds were permanent, why would melting and boiling take such different amounts of energy? The idea to reach is a statistical crowd of brief attractions.
A weak bond, in enormous numbers — Black’s ice and water experiment is described in his lectures, published after his death in 1803. His estimate of the latent heat of fusion was about 140 °F-degrees of water warming, against a modern 144. Dulong and Petit’s 1819 rule gives about 3R, 25 J/(mol·K), for solid elements. Liquid water’s 75 J/(mol·K), about 9R, includes rotation and the breaking of hydrogen bonds; ice’s 38 shows how much of that is the bonds.
Why those properties matter for life — High specific heat buffers organisms and coastlines against temperature swings, and the latent heat of vaporization makes sweating an effective coolant. Cohesion carries water up trees under tension, and floating ice insulates lakes. Each is a consequence of the same bonding.