Consider a reaction with a half-life of 20 minutes. If the amount of material remaining after 2 hours is 5 0 g 50 g, how much material was present at the start? ans in grams
To calculate the amount of material present at the start, we need to determine how many half-lives occurred during the 2-hour time period.
1 half-life = 20 minutes or 20/60 = 1/3 hours
2 hours = 2 x 60 minutes = 120 minutes = 4 half-lives
If the amount remaining after 4 half-lives is 50 grams, the initial amount present can be calculated using the formula:
Amount = Initial Amount x (1/2)^(number of half-lives)
50 = Initial Amount x (1/2)^4
50 = Initial Amount x (1/16)
Initial Amount = 50 x 16 = 800 grams
Therefore, the amount of material present at the start was 800 grams.