Reversible reactions in a sealed container
2 marks · EasyA reversible reaction occurs in a sealed container. At the start, there are 80 blue squares representing reactant molecules. Every second, one fifth of the blue squares turn yellow (product molecules). After one second, how many blue squares remain? Show your calculation.
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Show answer
64 blue squares remain after 1 second (±0)
Must show: shows calculation: (1/5) x 80 = 16; 80 - 16 = 64
Also accept: Calculation shown in any correct format resulting in 64
Common mistakes: Gives 80/5 = 16 as the final answer without subtracting; Calculates only new yellow, not remaining blue
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Correct calculation of number of blue squares that turn yellow (80/5 or 16).
A1 · 1 mark · Correct subtraction to find blue squares left (80 - 16 = 64).
Worked solution
Number of blue squares initially = 80.
One fifth of the blue squares turn yellow: (1/5) × 80 = 16.
Number of blue squares left: 80 - 16 = 64.