QQ登录
微博登录 
托福培训
托福考试动态
2017-02-16 13:03
来源：网络
作者：
Have you ever noticed that hot dogs are sold in packages of 10, while the buns come in packages of eight? In this scenario, the buns are the limiting reactant in the sense that they limit the hot dog preparation to eight. The limiting reactant or reagent is the one that is consumed first in the chemical reaction, and its consumption halts the progress of the forward reaction. When answering questions about limiting reagents on the exam, your first step should always be to convert all the masses you were given into moles. You should set up your table as you did before, only now you’ll have two amounts and thus two numbers of moles to get you started. Let’s look at a specific question, involving the Haber process. Basically, this is the process of making ammonia from the reaction of nitrogen and hydrogen gases. The reaction is shown below:Molar mass(28.02)(2.02)(17.04)
Balanced equation N2 +3H2 2NH3
No. of moles
Amount
Suppose you have a total of 25.0 kg of nitrogen to react with a total of 5.00 kg of hydrogen. What mass of ammonia can be produced? Which reactant is the limiting reactant? What is the mass of the reactant that’s in excess? Insert the masses in the correct rows and find the number of moles of both.
Molar mass(28.02)(2.02)(17.04)
Balanced equation N2 +3H2 2NH3
No. of moles892 mol2475 mol
Amount25,000 g5000 g
Start with nitrogen. You have 892 moles of it available, and in order for the nitrogen to react completely with hydrogen, you’d need 3(892 mol) = 2676 moles of hydrogen, which you don’t have. Therefore, hydrogen is the limiting reagent. Now let’s answer the other parts of the question. The mass of ammonia that can be produced is limited by the amount of hydrogen, so do your calculations based on the number of moles of hydrogen available. Your chart should look like the one below:Molar mass(14.02)(2.02)(17.04)
Balanced equationN2 +3H2 2NH3
No. of moles825 mol used2475 mol usedtherefore 1650 mol produced
Amount 892 mol 23,117 g used 25,000g 5000 g1650 mol (17.04) = 28,116 g produced
推荐阅读
新东方留学院校库，留学选校有门道
A BETTER YOU,A BIGGER WORLD!
版权及免责声明
①凡本网注明"稿件来源：新东方"的所有文字、图片和音视频稿件，版权均属新东方教育科技集团（含本网和新东方网） 所有，任何媒体、网站或个人未经本网协议授权不得转载、链接、转贴或以其他任何方式复制、发表。已经本网协议授权的媒体、网站，在下载使用时必须注明"稿件来源：新东方"，违者本网将依法追究法律责任。
② 本网未注明"稿件来源：新东方"的文/图等稿件均为转载稿，本网转载仅基于传递更多信息之目的，并不意味着赞同转载稿的观点或证实其内容的真实性。如其他媒体、网站或个人从本网下载使用，必须保留本网注明的"稿件来源"，并自负版权等法律责任。如擅自篡改为"稿件来源：新东方"，本网将依法追究法律责任。
③ 如本网转载稿涉及版权等问题，请作者见稿后在两周内速来电与新东方网联系，电话：010-60908555。
托福培训
托福考试动态
