CAIE A Level Chemistry 9701 · Group 17
The hydrogen halides , , and can be formed by direct combination of the elements. Samples of each hydrogen halide are heated in separate sealed tubes and the temperature at which each begins to decompose into its elements is recorded.
The decomposition temperatures are found to be in the order:
Compare the thermal stabilities of the hydrogen halides and explain the trend in terms of the strengths of the bonds between hydrogen and the halogen.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.
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