Mid Semester Test (Basic Chemistry)

1 (a) X is an element in my opinion, since we know that the elements are pure substances that can be decomposed again into other simpler substances by ordinary chemical reactions.
(b). Yes, the occurrence of physical changes in which no formation of new substances and the occurrence of endothermic reactions where the reaction requires heat energy gained or absorbed by the system of environmental
(c) yes X can be called as an element of us because they know that the elements are pure substances that can be decomposed again into other simpler substances by ordinary chemical reactions.

2. In this case does not fit with the law of conservation of mass to the sound of the mass conservation law is the law of conservation of mass, also known as the Lomonosov-Lavoisier law is a law that states the mass of a closed system is constant despite the wide range of processes in the system (in The mass of a closed system of substances before and after the reaction is the same (fixed / constant)). General statement used to declare the law of conservation of mass is the mass can change form but can not be created or destroyed. For a chemical process in a closed system, the mass of the reactants must equal the mass of the product, so if the mass is 10 grams of wax initially then after reacted with oxygen should be the result of the reaction must also be or remain 10 grams

3.The way to differentiate is with giving high energy so it can  break down so it can separate between one and other

4. Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table. Mendeleev was unaware of the other work on periodic tables going on in the 1860s. He made the following table, and by adding additional elements following this pattern, developed his extended version of the periodic table.^[10][11]

Cl 35.5	K 39	Ca 40
Br 80	Rb 85	Sr 88
I 127	Cs 133	Ba 137

On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that

1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.
2. Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
4. The elements which are the most widely diffused have small atomic weights.
5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring.
8. Certain characteristic properties of elements can be foretold from their atomic weights.

Mendeleev published his periodic table of all known elements and predicted several new elements to complete the table. Only a few months after, Meyer published a virtually identical table. Some consider Meyer and Mendeleev the co-creators of the periodic table, but virtually everybody^[who?] agrees that Mendeleev's accurate prediction of the qualities of what he called ekasilicon, ekaaluminium and ekaboron (germanium, gallium and scandium, respectively) qualifies him for the majority of the credit for the table.

For his predicted eight elements, he used the prefixes of eka, dvi, and tri (Sanskrit one, two, three) in their naming. Mendeleev questioned some of the currently accepted atomic weights (they could be measured only with a relatively low accuracy at that time), pointing out that they did not correspond to those suggested by his Periodic Law. He noted that tellurium has a higher atomic weight than iodine, but he placed them in the right order, incorrectly predicting that the accepted atomic weights at the time were at fault. He was puzzled about where to put the known lanthanides, and predicted the existence of another row to the table which were the actinides which were some of the heaviest in atomic mass. Some people dismissed Mendeleev for predicting that there would be more elements, but he was proven to be correct when Ga (gallium) and Ge (germanium) were found in 1875 and 1886 respectively, fitting perfectly into the two missing spaces.

5.White solid is precipitate is produced from the reaction of silver with mercury-added nitarat in klorida.Wjich is white solid formed new properties
Equation is HgCl+AgNO3 èHgNO3+AgCl

The Chemical Reaction

Hydrogen chloride vapor in the beaker and ammonia in a test tube reacts to form ammonium chloride cloud
The chemical reaction is a natural process that always results in a change kimia.Senyawa compounds or compounds involved early in the reaction is referred to as reactants. Chemical reactions are usually characterized by a chemical change, and will result in one or more products which typically have characteristics different from the reactants. Classically, chemical reactions involve changes involving the movement of electrons in the formation and breaking of chemical bonds, although the general concept is basically a chemical reaction can also be applied to the transformation of elementary particles such as in nuclear reactions.
Reactions with different chemical used in chemical synthesis to produce the desired compounds. In biochemistry, series of chemical reactions that are catalyzed by enzymes form metabolic trajectory, in which the synthesis and decomposition is usually not possible in the cell do.

Grouping of Chemical Reactions
The diversity of chemical reactions and approaches undertaken in the study resulted in the number of ways to classify these reactions, which often overlap. Below are examples of classification of chemical reactions that are usually used.
• isomerization, in which chemical compounds undergo structural rearrangement without any change in its atomic kompoasisi
• The combination of direct or synthesis, in which two or more elements or compounds unite to form a complex product:
N2 + 3 H2 → 2 NH3
• chemical decomposition or analysis, in which a compound is broken down into smaller compounds that:
2 H2O → 2 H2 + O2
• Replacement of single or substitution, characterized by an element is replaced by a more reactive element:
2 Na (s) + 2 HCl (aq) → 2 NaCl (aq) + H2 (g)
• metathesis or double replacement reaction, two compounds which change each other ions or bonds to form different compounds:
NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
• acid-base reactions, broadly speaking, is a reaction between the acid with a base. It has various definitions depending on the acid-base concept is used. Some of the most common definitions are:
 Definition of Arrhenius: acid dissociates in water releasing H3O + ions; bases dissociate in water releasing OH-ions.

The Brønsted-Lowry definition: Acids are proton donors (H +) donors; base is the recipient (acceptor) protons. Surrounding the Arrhenius definition.
 Lewis definition: Acids are electron pair acceptors; bases are electron pair donors. This definition encompasses Brønsted-Lowry definition.
 

Redox reactions, in which there is a change in oxidation number of atoms of compounds that react. This reaction can be interpreted as electron transfer. Examples of redox reactions are:
2 S2O32-(aq) + I2 (aq) → S4O62-(aq) + 2 I-(aq)
Which one is reduced to I-I2 and S2O32-(thiosulfate anion) is oxidized to S4O62-.
• Burning, is a kind of redox reaction in which the materials can be burned to join the elements of an oxidant, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used to refer only to the oxidation of a large scale in the whole molecule. Controlled oxidation at only one single functional group is not included in the combustion process.
C10H8 + 12 O2 → 10 CO2 + 4 H2O
CH2S + 6 F2 → CF4 + 2 HF + SF6
• disproportionation, with one reactant to form two types of products that differ only in oxidation state.
2 + → Sn Sn2 + + Sn4
• Organic Reactions, covering various types of reactions involving compounds which have carbon as its main element.

Chemical Kinetics

Reaction rate of a chemical reaction is a measurement of how the concentration or pressure of the substances involved in reactions change over time. Analysis of the reaction rate is very important and has many uses, for example in chemical engineering and chemical equilibrium studies. The rate of reaction is fundamentally dependent on:
• The concentration of reactants, which usually make the reaction go faster if the concentration is increased. This is caused due to an increase pertumbukan atoms per unit time,
• The surface area available for the reactants to interact with each other, especially the solid reactant in a heterogeneous system. Large surface area will increase the reaction rate.
• Pressure, with increasing pressure, we lowered the volume between molecules so that it will increase the frequency of molecular collisions.
• The activation energy, which is defined as the amount of energy needed to create a reaction that everything starts and goes spontaneously. Higher activation energy implies that the reactants need more energy to start the reaction than the reaction activation energy is lower.
• The temperature, which increases the reaction rate when raised, this is because high temperatures increase the energy of the molecule, thereby increasing inter-molecular collisions per unit time.
• The presence or absence of catalysts. Catalysts are substances that change the trajectory (mechanism) of a reaction and will increase the reaction rate by lowering the activation energy necessary for the reaction can be run. Catalysts are not consumed or changed during the reaction, so that it can be reused.
• For some reactions, the existence of electromagnetic radiation, especially ultraviolet, is needed to decide the bond required for the reaction can be everything starts. This mainly occurs in reactions involving radicals.
The rate of reaction is related to the concentration of substances involved in the reaction. This relationship is determined by the rate equation for each reaction. It should be noted that some reactions have a pace that does not depend on the concentration of the reaction. This is referred to as zero-order reaction.