Question

PRELAB QUESTIONS 1. Read the Background and Words You Should Know section carefully, and then, on a separate sheet or sheets of paper, define, in your own words, the following terms: a. chemical reaction b. chemical change c. physical change d. change of state e. reactant f. product g. aqueous h. solvent i. formula unit j. exothermic k. endothermic 1. exergonic m. endergonic 2. Write the chemical formulas for the following: h aluminum

Answer 1

1 )

a. Chemical reaction : A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.The reactants, are converted to one or more different substances, the products. Chemical reactions tend to involve the motion of electrons, leading to the formation and breaking of chemical bonds.A reaction can take place between two atoms or ions or molecules and they form a new bond and no atom is destroyed or created but a new product is formed from reactants.The rate of reaction depends on and is affected by factors like pressure, temperature, the concentration of reactants.

b. Chemical change : Chemical change is any change that results in the formation of new chemical substances. At the molecular level, chemical change involves making or breaking of bonds between atoms.Chemical changes are irreversible in nature.When a chemical change occurs, there is also a change in the energy of the system.During a chemical change, bonds between the molecules break and the composition of the substance change. In other words, chemical change leads to the breaking and making of bonds. Combustion, rusting, fermentation, etc. are a few examples of chemical change.

C. Physical change : Physical change is a type of change where the physical properties of matter change.A change of state of matter, change in colour, odour, solubility, etc. all are examples of physical change. During a physical change, neither the composition nor the chemical nature of matter is changed. During this change, molecules rearrange themselves without affecting the internal composition. A physical change doesn’t affect the chemical property.A common example of physical change is the conversion of states of water. Ice, water, and steam are the three physical states of water. But all the three forms contain H₂O.

d. A change of state is the change of a substance from one physical form of matter to another.Here energy must be added or removed.During a change of state, a substance gains energy from or loses energy to the environment,but the total amount of energy must be conserved.

e. Reactant : Reactant is a species which undergoes chemical change during a chemical reaction.They are the starting materials in a chemical reaction. Reactants undergo a chemical change in which chemical bonds are broken and new ones formed to make products.

f. Products : They are the species formed as a result of chemical reaction.During a chemical reaction reactants are transformed into products after passing through a high energy transition state. When represented in chemical equations products are by convention drawn on the right-hand side, even in the case of reversible reactions. Products are formed by the making and breaking of bonds.

g. Aqueous : Aqueous means it contains water.It is formed of matter deposited in or by water.

h. Solvent : A substance in which another substance is dissolved, forming a solution.It is the substance that can dissolve another substance, or in which another substance is dissolved, forming a solution. Water is the most common solvent.

i.Formula unit : A formula unit in chemistry is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound.

j. Exothermic : the term exothermic process (exo- : "outside") describes a process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light .Exothermic reactions may occur spontaneously and result in higher randomness or entropy (ΔS > 0) of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy (ΔH < 0). In the lab, exothermic reactions produce heat or may even be explosive.

k. Endothermic : There are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions. Endothermic reactions cannot occur spontaneously. Work must be done in order to get these reactions to occur. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. Endothermic reactions are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ΔH).

l. Exergonic :

• An exergonic reaction may be called a spontaneous reaction or a favorable reaction. Exergonic reactions release energy to the surroundings.The chemical bonds formed from the reaction are stronger than those that were broken in the reactants. The free energy of the system decreases. The change in the standard Gibbs Free Energy (G) of an exergonic reaction is negative (less than 0).The change in entropy (S) increases. Another way to look at it is that the disorder or randomness of the system increases.Exergonic reactions occur spontaneously (no outside energy is required to start them).

m. endergonic :

• Endergonic reactions may also be called an unfavorable reaction or nonspontaneous reaction. The reaction requires more energy than you get from it.Endergonic reactions absorb energy from their surroundings.The chemical bonds that are formed from the reaction are weaker than the chemical bonds that were broken.The free energy of the system increases. The change in the standard Gibbs Free Energy (G) of an endergonic reaction is positive (greater than 0).The change in entropy (S) decreases.
• Endergonic reactions are not spontaneous.Examples of endergonic reactions include endothermic reactions, such as photosynthesis and the melting of ice into liquid water.If the temperature of the surroundings decreases, the reaction is endothermic.

2) a. Copper - Cu

b. Aluminium - Al

c. Hydrochloric acid - HCl

d. Magnesium sulfate - MgSO₄

e.Copper(II)chloride - CuCl₂

f.Sodium bicarbonate - NaHCO₃

g.Sodium hydroxide - NaOH

h. Methane - CH₄

i. Hydrogen - H

j.Sodium chloride - NaCl

k. Carbon dioxide - CO₂

l.Oxygen - O

m. Calcium carbonate - CaCO₃

n. Magnesium hydroxide - Mg(OH)₂

o. Aluminium chloride - AlCl₃

p.Sodium carbonate - Na₂CO₃

q. Calcium chloride - CaCl₂

r. Water - H₂O

s. Sodium - Na

t. Carbon monoxide - CO

u.Sulfur - S

v. Iron - Fe

w.Iron(II)sulfide - Fe₂S

x.Magnesium chloride - MgCl₂

y. Sulfuric acid - H₂SO₄

z. Sodium sulfate - Na₂SO₄

3)

Cu(NO₃)₂ - Copper(II) nitrate

CuCO₃ - Copper(II) carbonate

KCl (aq) - Aqueous potassium chloride

KBr (aq) - Aqueous potassium bromide

Cl₂ - Chlorine molecule

Br₂ - Bromine molecule

HBr (aq) - Aqueous hydrogen bromide

KOH (aq) - Aqueous potassium hydroxide

NaNO₃ - Sodium nitrate

AgCl - Silver chloride