CHEM 1201 Chapter : Chapter 3 Lecture Class

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15 Mar 2019

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Balancing equations: the products of a chemical reaction have to account for all the atoms present in the reactants. Matter can"t be lost in a chemical reaction: when balancing a chemical equation we adjust the stoichiometric coefficients in front of chemical formulas, subscripts in a formula are never changed when balancing an equation. It appears as though h has been lost and o has been created then the reaction is unbalanced. To balance the equation we adjust the stoichiometric coefficients. If the reaction looks easy just balance it by inspection. General guidelines: on either side, start with the molecule that has the most atoms, first balance the most numerous atom in that molecule followed by the 2nd and so on. If a fraction is required to finally balance the reaction, use one but you must get rid of the fraction by multiplying through the entire reaction by the appropriate coefficient! 1 al, 1 h and 1 cl unbalanced.

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I need help doing my lab homework, I missed lab that day because, I was sick and it's due.

Chemical Reactions and Equations Learning objectives To observe physical and chemical properties associated with chemical changes To be able to give evidence for the occurrence of a chemical reaction To write a balanced chemical equation To identify areaction as a combination, decomposition, precipitation, single or double replacement, or combustion reaction ntroduction When a substance undergoes a physical change, it changes its appearance but not its composition. For example, when ice melts to form water, it undergoes a physical change from solid to liquid. In a chemical change, the composition of a substance is changed to give a new substance with different physical and chemical properties. For example, when silver tarnishes, the shiny silver (Ag) changes to a dull gray silver sulfide (AgaS). Not only has the chemical formula changed from Ag to Agus, but also the physical properties (shininess) of the substance have changed. Some examples of physical and chemical changes are listed in Table 1 below. Table 1. Comparison of Physical and Chemical Changes Examples of Physical changes Examples and Evidence of Chemical Changes Change in state (melting, freezing, evaporating Formation of a gas (bubbles) subliming) Formation of a solid (precipitate) Change in size Tearing Change in Color Heat is given off or absorbed A solid dissolving in a solvent In a chemical reaction, atoms in the reactants are rearranged to produce new combinations of atoms in the products. However, the total number of atoms of each element in the reactants is equal to the total number of atoms in the products. This is true according to the Law of Conservation of Mass, which states that the total mass remains constant during a chemical reaction. In other words, matter cannot be created or destroyed in a chemical reaction. In a chemical equation, the reactants are shown on the left and the products are on the right. An arrow in between indicates that a chemical reaction occurs. Finally, the physical state of each compound is designated in parentheses after the chemical formula. Solid, liquid, gas, and aqueous (dissolved in water) are shown as(s,(n,(g), and (aq), respectively.

CHM111

Q1. Which of the following contains the MOST atoms? You shouldn't need to do a calculation here.

A) 10.0 g Ne

B) 10.0 g He

C) 10.0 g Ar

D) 10.0 g Kr

E) 10.0 g Mg

Q2. How many atoms are present in 0.23 moles of Calcium?

Q3. How many atoms are present in 5.6 mg of Silicon?

Q4. How many grams of iodine do 5.6 x 10²⁵ atoms of iodine represent?

Q5. Balance the following Chemical Equations:

_____ CaC₂(s) + _____H₂O(l) ? _____ Ca(OH)₂(aq) + _____ C₂H₂(g)

_____ P₄O₁₀ + _____ H₂O? ______ H₃PO₄

___ C₃H₈O₃ + ___ O₂ ? ___ CO₂ + ___ H₂O

_____ C₄H₁₀(l) + _____ O₂(g) ? _____ CO₂(g) + _____ H₂O(g)

___ Al + ___ N₂ ? ___ Al₂N₃

___ NaN₃ ? ___ Na + ___ N₂

___ C₃H₅N₃O₉ ? ___ CO₂ + ___ N₂ + ___ H₂O + ___ O₂

Q6. Calculate the percent composition of each element in Al(NO₃)₃

Q7. A 65.0 g sample of a pure compound containing only Nickel, Oxygen and Carbon is found to contain 22.36 g Nickel and 18.27 g Carbon. What is the empirical formula of compound?

Q8. Determine the Empirical formula and Molecular formula of a compound that contains: 65.4% C, 9.15% H and 25.4% N by mass and has a molar mass of 220 g/mol.

Q9. Oxygen gas can be produced by the decomposition of KClO₃

2KClO₃ (s) ? 2 KCl + 3 O₂ (g)

How many grams of O₂ can be produced from 1.625 g of KClO₃?

Q10. Consider the following balanced reaction: 2 Fe (s) + Al₂O₃ (s) Â® 2 Al (s) + Fe₂O₃ (s)

If 6.25 moles of Fe react with 2.50 moles of Al₂O₃

Which reactant is the limiting reagent?

How many grams of Al are produced?

Q11. Consider the reaction for the manufacture of Aluminum sulfate:

2 AlCl₃ (aq) + 3 H₂SO₄ (aq) ? Al₂(SO₄)₃(aq) + 6 HCl (aq)

If 15.0 g of AlCl₃was mixed with 25.0 g of H₂SO₄, which reactant is the limiting reagent?

Calculate the theoretical yield of Al₂(SO₄)₃.

If only 18.63 g of Al₂(SO₄)₃ was produced, what is the percent yield of Al₂(SO₄)₃?

Q13. How many grams of Nickel (II) chloride are needed to prepare 100.0 ml of 0.125 M solution?

Q14. What volume of 0.125 M KMnO₄ (aq) solution can be prepared from 12.623 g of KMnO₄?

CHEM 1201 Chapter : Chapter 3 Lecture Class

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