Topics in ChemistryGas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases Avogadro'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
Academic Questions in Chemistry
With regards to redox reactions, which of the following statement is wrong?
A. Redox reaction are examples of chemical change
B. Reduction is the gain of electron
C. Substances that donates election during chemical reaction are termed reductants
D. Oxidizing agents are always reduced in chemical reactions
E. Oxidation occurs at the cathode in electrolysis
F. Hydrogen is a reducing agent
In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.
_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.
_____ is the negative electrode in electrolysis.
The above diagram shows the _____ type of bond.
B. Polar covalent
C. Coordinate covalent
E. Van dear walls
Metals are referred to as _____ in their impure state.
Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.
The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.
D. Number of moles
F. Amount of substance
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:
|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
Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years
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
Below are the physical properties of metals:
They exist in solid state.
The have high densities.
They are good conductors of heat and electricity.
The have the ability to be polished, to glow, sparkle and reflect light.
They can be bent, flattened and made into sheets called foils.
They can be drawn into wires.
Iron undergoes magnetism while most metals are poorly magnetized.
They typical have high melting point.
They generally have high boiling point.
With the exception of lithium, sodium and potassium, most metals are generally hard.
They have the ability to make sound when in contact with other objects or metals.
John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.
Below are Dalton's Atomic Theory:
All matter consists of tiny indivisible particles called atoms.
Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.
Atoms are indestructible and can neither be created nor destroyed.
Atoms of different elements can combine with each other in simple whole number ratios to form compounds.
Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.
Meanwhile, understand that the above theories of John Dalton had been modified.
The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.
Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.
The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.
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)
Step 1: Identify the given parameter from the question.
Fe = 69.94%, O = 30.06%.
Empirical formula = Fe?O?
Step 2: Convert the percentages to gram. (just attribute grams to the %).
Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.
Mole of Fe: 69.94/55.85 = 1.252mol
Mole of O: 30.06/16 = 1.879mol
Step 4: Divide both sides by the smallest mole ratio.
Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1, 1.879/1.252 = 1.5
We now have the formula = Fe1O1.5
Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.
For iron (Fe), we will have 1 x 2 = 2
For oxygen (O), we will have 1.5 x 2 = 3
Step 6: Write the empirical formula.
The empirical formula= Fe2O3
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: