Chemical Reactions and Equations Learning objectives To observe physical and che

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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.

Explanation / Answer

A:Magnesium and Oxygen:

Data analysis:

Initial appearance of Mg --> Shiny gray solid

Observation during reaction --> Formation of highly dazzling flame

4: The balanced equation is

2Mg(s) + O2(g) ----> 2MgO(s)

5: Since Mg and O2 are combined to form a new product, MgO, this is a Combination reaction.

This is also a combustion reaction, as Mg reacts with O2 to form oxide.

B:Zinc and copper(II) sulfate:

Data analysis

Zn --> Gray solid

CuSO4 ---> Blue

after 15 min ---> Zn gradually becomes black and blue color gradually fades

After 30 min --> The solution becomes colorless

5: Zn(s) + CuSO4(aq) ----> Cu(s) + ZnSO4(aq) --- already balanced.

6: Since only Zn is repalced by Cu2+, this is a single displacement reaction.

C. Metals and HCl:

Data analysis:

6: The balanced reactions are

Cu(s) + 2 HCl(aq) --- > CuCl2(aq) + H2(g)

Zn(s) + 2 HCl(aq) --- > ZnCl2(aq) + H2(g)

Mg(s) + 2 HCl(aq) --- > MgCl2(aq) + H2(g)

7: Single displacement reaction in all the cases.

D: Reaction of ionic compounds:

Data analysis:

5: 3CaCl2(aq) + 2Na3PO4(aq) ---> Ca3(PO4)2(s) + 6NaCl(aq)

BaCl2(aq) + Na2SO4(aq) ----> BaSO4(s) + 2NaCl(aq)

FeCl3(aq) + 3KSCN(aq) ----> Fe(SCN)3(s) + 3KCl(aq)

6: Double displacement reaction in all cases

E: Sodium carbonate and HCl:

Balanced chemical reaction:

2HCl(aq) + Na2CO3(s) ----> CO2(g) + H2O(l) + 2NaCl(aq)

Decomposition reaction

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