Chemistry Past Questions and Answers

Which of the following is a physical change?

In a reaction: \(SnO_{2} + 2C → Sn + 2CO\) the mass of coke containing 80% carbon required to reduce 0.302 kg of pure tin oxide is?<br/>(Sn - 119, O - 16, C - 12).

Cr<sub style='font-size: smaller;'>2</sub>O<sub style='font-size: smaller;'>7</sub> + 6Fe<sup style='font-size: smaller;'>2+</sup> + 14H<sup style='font-size: smaller;'>+</sup> → 2Cr<sup style='font-size: smaller;'>3+</sup> +6Fe<sup style='font-size: smaller;'>3+</sup> + 7H<sub style='font-size: smaller;'>2</sub>O. In the above , the oxidation number of chromium changed from?

In the reaction 1O<sup style='font-size: smaller;'>-</sup><sub style='font-size: smaller;'>3</sub> + 5l<sup style='font-size: smaller;'>-</sup> + 6H<sup style='font-size: smaller;'>+</sup> → 31<sub style='font-size: smaller;'>2</sub> + 3H<sub style='font-size: smaller;'>2</sub>O, the oxidizing agent is?

Fe\(_2\)O\(_{3(s)}\) + 2Al\(_{(s)}\) → Al\(_2\)O\(_3\) + 2Fe\(_{(s)}\). If the heats of formation of Al\(_2\)O\(_3\) and Fe\(_2\)O\(_3\) are - 1670 kJmol\(^{-1}\) and - 822 kJmol\(^{-1}\) respectively, the enthalpy change in kJ for the reaction is ?