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
Charles's law, sometimes referred to as the law of volumes, show the effects of absolute temperature on the volume of a gas at constant pressure. This absolute temperature must be measured with the kelvin scale, and not the celcius scale. This is so because the zero value on the kelvin scale corresponds to a complete stoppage of molecular motion; that is, the ideal gas particles becomes fixed in a position, just like solid particles.
The details of Charles's law emphasizes on the expansion of a gas when its temperature is increased at a constant pressure, and its subsequent contraction when the temperature is reduced. In this regard, when a gas becomes heated, its volume increases, and when cooled, the volume decreases proportionately. This is shown below:
From the above image, we can see that the gas occupied a lesser volume (V1) at a lower temperature (T1).
At a higher temperature (T2), the volume occupied by the gas (V2) increases proportionately. We can therefore infer that temperature and volume are directly proportional in the sense that when one (temperature) increases, the other (volume) increases accordingly, and vice versa.
Absolute temperature refers to the temperature of an object or a substance on the kelvin scale where zero is taken as absolute zero. This zero point implies that the particles (or molecules) making up the substance exhibit their minimum motion. In short, a substance becomes solid at this temperature and can no longer become colder.
The absolute zero temperature on the celcius scale is -273.15oC. However, calculations involving Charles's law must be solved using the kelvin temperature. In order to convert celsius to kelvin temperature, the value '273.15' should be added to the celcius temperature. For example, if we were to convert 100oC to kelvin temperature, it becomes '100 + 273.15' = 373.15K.
The graph below shows Charles's law through the celsius scale.
At the absolute zero temperature; that is, zero kelvin or -273.15oC, notice that the volume occupied by the gas is zero (when traced to the right, as shown in the above graph). As the temperature increases, the volume also increases. This is further explained through the kelvin scale (graph) below:
From the above graph, notice that the temperature is measured in kelvin. At absolute zero temperature (zero kelvin or 0K), the volume occupied by the gas equals zero. As the temperature increases, the volume also increases proportionately. Therefore, Charles's law uses a straight line graph running through 0 kelvin or -273.15oC to represent the relationship between the volume and temperature of a gas (at constant pressure).
Charles's law states that the volume of a given mass of gas is directly proportional to the absolute temperature of the gas, provided the pressure remains constant.
The French physicist, Jacques Charles (1746-1823) formulated this law in 1780.
Charles's law may also be restated that the kelvin temperature and volume will always be in direct proportion if the pressure exerted on a dry gaseous sample remain constant.
With reference to Charles's law, the following equations are derived:
V = T
V/T = k (constant )..... Equation 1
V = Volume, T = Temperature and k = Constant
The value of k is dependent on the pressure of gas, amount of the gas and the unit of gas measurement.
Increase in Volume = Increase in Temperature
Increase in V1 = Increase in T1
Increase in V2 = Increase in T2
V1 = Initial Volume
T1 = Initial Temperature
V2 = Final Volume
T2 = Final Temperature
Substituting into Equation 1
V1/T1 = V2/T2..... Equation 2
V1 T2 = V2 T1..... Equation 3
Various instances of Charles's law have been observed on substances, objects or processes at different temperatures. Examples are:
Baking of bread
Deodorant sprays, insecticides and perfumes
Dented table tennis ball
Hot air balloon
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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: