Chemistry - Stoichiometry

--- title: Chemistry - Stoichiometry image: robots: noindex, nofollow lang: zh --- # Chemistry - Stoichiometry ==**[Index]**== [TOC] ## What is Stoichiometry? >Stoichiometry is a kind of calculation of reactants and products in chemical reactions. **What you will learn.** + Chemical Formula + Chemical Equation + Calculation of Chemical Reaction + Problem practice ## Chemical Formula :::warning A **Chemical Formula** is a way of presenting information about the chemical proportions of atoms. ::: ### 1. Empirical formula(最簡式) > *Empirical formula(最簡式又稱實驗式、簡式)* is a **simple expression of the ratio of the elements in the compound**. > (數字化簡，元素合併) :::success + **Example** Octane has a **molecular formula of C~8~H~18~**, or structurally CH~3~CH~2~CH~2~CH~2~CH~2~CH~2~CH~2~CH~3~, meaning that Octane is a chain structure of 8 carbon atoms, and 18 hydrogen atoms. Simplify it into **empirical formula, C~4~H~9~ .** + :+1: **Why Empirical formula?** * To get simple ratio of the elements in the compound * Yielded after "Elemental Analysis" + :-1: **Empirical formula is not unique.** That means we can't confirm that an empirical formula, for example, C~4~H~9~, is the expression of C~8~H~18~ or C~12~H~27~ or C~16~H~36~... ::: ### 2. Molecular formula(分子式) > *Molecular formula(分子式)* indicates the **simple numbers of each type of atom in a molecule of a molecular substance**. > (數字**不**化簡，元素合併) :::success + **Example** Octane has a **molecular formula of C~8~H~18~** . + :+1: **Why Molecular formula?** * To get "**exact**" numbers of each type of atom in a molecule + :-1: **Molecular formula is not unique.** For example, C~2~H~6~O can be an expression of methoxymethane(Methyl ether, 二甲醚，又稱甲醚) or ethanol(alcohol). Both of them have a molecular formula of C~2~H~6~O, there's no way to distinguish between them without further information. **Using molecular formula can't indicate the specific chemical compound.** ::: ### 3. Condensed formula(簡縮結構式, 示性式) most-used > *Condensed formula(簡縮結構式)* represents the types and spatial arrangement of bonds in a simple chemical substance. > (數字**不**化簡，元素**不**合併) :::success + **Example** methoxymethane : CH~3~OCH~3~ ethanol : C~2~H~5~OH Expressed in Condensed formula allows us to indicate the specific chemical compound. + :+1: **Why Condensed formula?** + To distinguish specific chemical compound + :-1: May request more background knowledge about chemistry. ::: ### 4. Structural formula(結構式) > The *Structural formula(結構式)* of a chemical compound is a graphic representation of the molecular structure. > (數字**不**化簡，元素**不**合併，畫圖!!!) :::success + **Example** methoxymethane <img src="https://upload.wikimedia.org/wikipedia/commons/4/4f/Dimethylether_structure.png" style="width:200px;"> ethanol <img src="https://upload.wikimedia.org/wikipedia/commons/e/e8/Ethanol-structure.svg" style="width:200px;"> + :+1: **Why Structural formula?** + To get a rough relative position of atoms in the compound + To distinguish specific chemical compound + :-1: May request more background knowledge about chemistry. + :-1: The structure **does not display the real position accurately.** ::: ## Chemical Equation See [Chemistry 1-3 - Chemical Reaction & Equations](https://hackmd.io/@RxnNode/By2w9SqjS#Chemical-Reaction-amp-Equations) ## Calculation of Chemical Reaction ### :star2: Calculation Toolkit * [Law of conservation of mass](https://hackmd.io/@RxnNode/By2w9SqjS#Law-of-Conservation-of-Mass) * [Balancing Chemical Equations SOP](https://hackmd.io/@RxnNode/By2w9SqjS#2-Balancing-Equations-SOP) * Molar ratio * Grams to moles * Moles to grams --- ### 1. [Law of conservation of mass](https://hackmd.io/@RxnNode/By2w9SqjS#Law-of-Conservation-of-Mass) ### 2. [Balancing Chemical Equations SOP](https://hackmd.io/@RxnNode/By2w9SqjS#2-Balancing-Equations-SOP) ### 3. Molar ratio > The simple ratio of balanced Chemical Equations :::info + **Example:** CH~4~ + 2O~2~ $\to$ CO~2~ + 2H~2~O **Molar ratio:** 1 : 2 : 1 : 2 + **What does that mean?** 1. The reaction consumes the reactants in the molar ratio of 1 : 2 2. The reaction produces the products in the molar ratio of 1 : 2 3. If reactants and products are gases then the ratio represents the ratio of volume as well(ideal gas) ::: :::danger **TL;DR** + **Molar ratio** = The **amount ratio** of the reactants consumed and the products produced + If all substance are gases then **molar ratio = volume ratio(ideal gas)** ::: ### 4. Grams to moles $$ Moles = { Mass(grams) \over Molar Mass} $$ ### 5. Moles to grams $$ Mass(grams) = { Moles \times Molar Mass} $$ ## Problems ### Question 1 :::info How many moles of ZnCl~2~ will be produced from 65.0$\text{g}$ of Zn and HCl, assuming HCl is available in excess?(Zn = 65) ::: :::spoiler Hint 1. Write down the equation 2. Balance the equation 3. Calculate mole using molar ratio ::: ### Question 2 :::info **Add 72$\text{g}$ of water into Calcium carbide(CaC~2~)96$\text{g}$ to produce Ethyne (C~2~H~2~), answer the question below:** 1. Which chemical compound is limiting reagent? 2. How many grams of limiting reagent left? 3. How many moles of Ethyne will be produced(ideal)? 4. In conditions of STP. If the reaction is not ideal. We only collected 22.4L of Ethyne. What is the yield rate? ::: ### Question 3 :::info Balance the eqaction below: 1. Na + H~2~O $\to$ (guess the products) 2. Ca(OH)~2~ + HCl $\to$ (guess the products) 3. C~6~H~12~O~6~ + O~2~ $\to$ (guess the products) 4. KOH + H~3~PO~4~ $\to$ (guess the products) 5. CaCl~2~ + Na~3~PO~4~ $\to$ (guess the products) 6. FeS + O~2~ $\to$ (guess the products) ::: ### Question 4 :::info >**Ester**, a kind of organic chemical compound, derived from a carboxylic acid and an alcohol. You might recognize it by its aromatic smell. **Isoamyl acetate**(乙酸異戊酯，又稱香蕉油), having an odor of banana, is formed from isoamyl alcohol and acetic acid. **(CH~3~)~2~CHCH~2~CH~2~OH + CH~3~COOH $\to$ C~7~H~14~O~2~ + H~2~O** Now, We combine 30g of acetic acid and 22g of isoamyl alcohol with a little bit of H~2~SO~4 and heat all of them to form isoamyl acetate. 1. Which chemical compound is limiting reagent? 2. In an ideal condition, how many grams of isoamyl acetate will be yielded? 3. However, after reactants fully reacted, we only collected 18g of isoamyl acetate. What is the yield rate? ::: ### Question 5 :::info > **Silver** is a chemical element that tarnishes in contact with sulfur. In the ancient time of China, silver-based tableware is used in the royal family to detect Arsenic trioxide(砒霜, As~2~O~3~) which is not sulfur-based poison but contain sulfur due to immature production processes. Nowadays, We wear silver as adornment forgetting it will turn black in contact with sulfur and enjoying the hot spring :) The tarnishing reaction as below: **Ag~(s)~＋H~2~S~(g)~＋O~2(g)~ $\to$ Ag~2~S~(s)~＋H~2~O~(ℓ)~(Not balaced)** If 2.70g of Ag, 1.70g of H~2~S, and 0.16g of O~2~ are mixed evenly，and they reacted fully.（O＝16，S＝32，Ag＝108） 1. Which chemical compound is limiting reagent? 2. How many grams of the black matter(Ag~2~S) will be yeilded? ::: ###### tags: `Chemistry` `Book`