At normal atmospheric pressure, solid carbon dioxide (dry ice) sublimes at −78 ∘C-78\,^\circ\mathrm{C}−78∘C. A block of dry ice at −90 ∘C-90\,^\circ\mathrm{C}−90∘C is placed in a room at 20 ∘C20\,^\circ\mathrm{C}20∘C. Which describes what happens to the dry ice?
It warms to −78 ∘C-78\,^\circ\mathrm{C}−78∘C, melts, and then the liquid boils
It warms to −78 ∘C-78\,^\circ\mathrm{C}−78∘C, then stays at −78 ∘C-78\,^\circ\mathrm{C}−78∘C as it sublimes
It turns to gas at −90 ∘C-90\,^\circ\mathrm{C}−90∘C without its temperature changing
Its temperature rises steadily to 20 ∘C20\,^\circ\mathrm{C}20∘C as it turns to gas
84 exam-style questions on Edexcel GCSE Chemistry 3.1 States of matter, covering 3.1.1 The three states of matter and changes of state. Each one has a worked solution and a mark scheme showing where the marks go.