B2 中高級 美國腔 44

 In this problem, we're given the concentration of a reactant inside of a porous catalyst sphere for three different catalysts. Same diameter, but the concentration profiles are significantly different, and the question is, which one of these catalysts is going to react the largest amount of reactant in a given time? It's the same reaction, and we also require to indicate any assumptions. So there's not really sufficient information to answer this. We can make some assumptions, and depending on which assumptions we make, we can end up with different answers. So one assumption is that the rate constant is the same. Well if we make this assumption, then it's easy to determine that catalyst 1 reacts the most, because the amount that reacts is going to be the rate constant times the concentration inside the catalyst, and since the concentration is changing we integrate over the volume of the catalyst. Each catalyst has the same volume, so if the rate constant is the same, the one with the highest concentration is going to have the highest rate, and so that's catalyst 1. The other extreme would be to assume that the diffusivities are the same for each of the catalysts. This means the rate constants are different, and now the catalyst with the highest rate is going to be catalyst 3 because the gradient, diffusivity times the change in concentration of A with respect to radius evaluated at the external surface, evaluated here, for how much is diffusing into the catalyst because whatever diffuses in reacts. If the diffusivity is the same then the one with the largest gradient, which is catalyst 3 has the largest gradient here, and therefore the most is diffusing in, and so this would say the k3 is larger than k2, larger than k1, and therefore the most that reacts now is in catalyst 3. So you can see, just from these concentration gradients comparing different catalyst, we need more information to reach a conclusion as to which is reacting the most material per time.

# 反應動力學-範例一 (Kinetics Exam Review 1A)

44

1. ## 1. 單字查詢

在字幕上選取單字即可即時查詢單字喔！

2. ## 2. 單句重複播放

可重複聽取一句單句，加強聽力！

3. ## 3. 使用快速鍵

使用影片快速鍵，讓學習更有效率！

4. ## 4. 關閉語言字幕

進階版練習可關閉字幕純聽英文哦！

5. ## 5. 內嵌播放器

可以將英文字幕學習播放器內嵌到部落格等地方喔

6. ## 6. 展開播放器

可隱藏右方全文及字典欄位，觀看影片更舒適！

1. ## 英文聽力測驗

挑戰字幕英文聽力測驗！

1. 點擊展開筆記本讓你看的更舒服

1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯，不妨使用「俚語字典」，或許會讓你有滿意的答案喔