iGCSE Chemistry (0620) Core:6.2 Rate of reaction: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
On a graph of gas volume against time, the rate of reaction at any particular moment is shown by how steep the curve is at that point—the steeper the tangent, the faster the reaction. Point A sits on the steepest part of the upper curve, right at the start where the slope is sharp and the reaction is going full speed. The other points are on much flatter sections, meaning the reaction has slowed down significantly by the time it reaches those points.
▶️ Answer/Explanation
Detailed solution:
The fastest rate means the largest volume of hydrogen is produced per second. Let’s check the volume changes: 0–30s: 32 cm³ produced (average ~1.07 cm³/s). 30–60s: 59 − 32 = 27 cm³. 60–90s: 68 − 59 = 9 cm³. 90–120s: 74 − 68 = 6 cm³. The largest change is in the first 30 seconds (32 cm³), so the rate is fastest in the 0–30 second period.
▶️ Answer/Explanation
Detailed solution:
A catalyst works by providing an alternative reaction pathway with a lower activation energy, which speeds up the rate of reaction. Crucially, the catalyst itself is not consumed during the reaction – it remains chemically unchanged. Therefore, its mass is exactly the same before and after the reaction. A catalyst does not change the overall enthalpy change (so it does not make the reaction more exothermic), does not affect the final yield of products, and is definitely not used up.