Topics in ChemistryAvogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures What are mixtures? Characteristics of mixtures Physical properties of matter Chemical properties of matter explained with examples Differences between physical and chemical change in chemistry Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid state of matter: Characteristics of liquids Gaseous state of matter: Characteristics of gases Molar Mass, worked examples and differences with molecular mass
Academic Questions in Chemistry
Which of the following isn't an element of the periodic table.
According to the periodic table, elements in the same group have got the same number of shells.
The periodic table of elements is also called the Mendeleev's table.
The simplest formula of a compound is termed _____.
A. Emperical formula
B. Molecular formula
C. Avogadro's number
D. Mass formula
E. Molar mass formula
F. Mole ratio
A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)
Which of the following statement is false concerning hydrocarbons?
A. Hydrocarbons can be aromatic
B. Hydrocarbons are made up of carbon and hydrogen only
C. Alkynes are aliphatic hydrocarbons
D. Alkenes have a carbon-carbon double bond in their structure
E. Benzene ring has a carbon-carbon triple bond in its structure
F. Hydrocarbons are the main constituents of petroleum and natural gas
The ability of carbon to form long chain of itself is called _____.
A. Carbon chain reaction
E. Organic chemistry
F. Carbon moleculation
Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).
A. 13.00894 amu
B. 11.00206 amu
C. 12.00794 amu
D. 14.001 amu
E. 15.001 amu
F. 16.033 amu
In English language, dynamic means 'changing' while static means 'no movement'.
In chemistry, static equilibrium (also called mechanical equilibrium) involves an interacting system or reaction whereby there isn't any movement of molecules between the reactants and products. Such reaction is said to be complete since the rate of reaction becomes zero.
An instance of static equilibrium is seen when diamond (an allotrope of carbon) is converted to graphite, another allotrope of carbon.
Graphite is a more stable allotrope of carbon, making it almost impossible to become converted into diamond. However, diamond may still be converted into graphite but at a very high activation energy. To this end, it must be heated above 2000°C before it show signs of convertion into graphite. This therefore implies that without an application of temperature (heat), the conversion process of diamond into graphite will likely take billions of years at room temperature. See the equation below:
C(s) (diamond) -> C(s) (graphite)
From the above equation, we can safely say that both allotropes of carbon (diamond and graphite) exists in static equilibrium since their reaction rate is effectively zero at room temperature.
Static equilibrium is typically unidirectional in nature. In fact, when a unidirectional reaction uses all its limited reactants, static equilibrium is said to be reached because the backward reaction cannot proceed, thus bringing the reaction rate to zero. We can therefore conclude that such reaction is ended at this point.
In physics, when the forces acting on an object nullifies each other, thus bringing about a constancy of content (that is, content remains the same in composition and without any form of movement), then static equilibrium is said to be reached.
The image shows a system in static equilibrium:
Dynamic equilibrium (also called chemical equilibrium) is defined as a state whereby the rate of forward reaction equals that of the backward reaction even though the movement of substances still occurs between both (reactants and products). In addition, the concentration of the reactants and products remains constant with time while the system shows no further change in properties.
Dynamic equilibrium will always occur in a reversible chemical reaction (denoted by ⇌).
The images below shows a summary of how a system in dynamic equilibrium (chemical equilibrium) works
However, since dynamic equilibrium is reversible in nature, it will therefore occur only in closed systems while using chemical reactions as a point of reference; unlike static equilibrium which may take place in both open and closed systems.
The table below summarizes the differences between static and dynamic equilibrium:
|Static Equilibrium||Dynamic Equilibrium|
|The reaction ends. There isn't any further reaction in the system||Chemical reaction between the reactants and products are still ongoing at equal rates|
|It can occur in both open and closed systems||It occurs only in closed systems|
|The reaction is irreversible in static equilibrium||The reaction is always reversible in nature|
|The rate of reaction is zero, thus such reactions are completed||The forward and backward reaction rates are always equal|
|Static equilibrium is always explained in mechanical processes. For this reason, it's also called mechanical equilibrium||Dynamic equilibrium is always explained in chemical processes. For this reason, it's also called chemical equilibrium|
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Amazing facts in Chemistry
The only letters that failed to appear on the periodic table are letters:
Gold and copper are the only two non-silvery colored metals.
Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools
Water freezes faster when it’s warm than when it’s cold
Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy
If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.
Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre
NOTABLE POINTS IN Chemistry
In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.
Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:
They are shown in the image below:
It's important to note the followings:
Alkanes have single bonds (only) in their structures.
Alkenes always have a carbon-carbon double bond present in their structure.
Alkynes always have a carbon-carbon triple bond present in their structure.
Aromatic hydrocarbons are classified into:
Organic chemistry is the study of carbon and it's compounds.
Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.
A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.
Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.
The large molecules (above) have no specific chemical formula throughout their volume.
Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.
Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)
Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen
Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.
12.001 + (1.00794 x 4)
Molecular Mass of Methane = 16.033 amu
Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)
Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen
Water contains 2 atoms of Hydrogen and 1 atom of oxygen.
(1.00794 x 2) + 15.9994
Molecular Mass of Water = 18.015 Da
Below are some facts about gold:
It is the only metal that has a gold (golden) color
Gold is present inside the earth crust in all the seven continents
Pure gold is soft and very stretchable (It can even be stretched into threads)
The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'
Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables
Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants
The term Gold originated from an ancient English word 'geolu' which means yellow
24karat gold is the purest gold element