| Date | May 2015 | Marks available | 1 | Reference code | 15M.1.hl.TZ1.20 |
| Level | HL | Paper | 1 | Time zone | TZ1 |
| Command term | Question number | 20 | Adapted from | N/A |
Question
Which statement about a first-order reaction is correct?
A. The reactant concentration decreases linearly with time.
B. The reactant concentration decreases exponentially with time.
C. The rate of reaction remains constant as the reaction proceeds.
D. The rate of reaction increases exponentially as the reaction proceeds.
Markscheme
B
Examiners report
Students found this question to be somewhat difficult with 42.15% correct answers. However, almost 40% of the candidates chose A, namely that for a first-order reaction, the reactant concentration decreases linearly with time (rather than exponentially); this suggests the importance of reading the statements more thoroughly.
Syllabus sections
Additional higher level (AHL) » Topic 16: Chemical kinetics » 16.1 Rate expression and reaction mechanism
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