Chemical Reactions Cheat Sheet
Changes in the chemical structures of the matters are called chemical changes. Atoms or molecules of matter interact with each other in these changes. In general, bonds, keeping atoms or molecules together, are broken and after chemical change, new bonds are produced between atoms or molecules.
"Chemical reactions" are symbolization of chemical changes with element/compounds symbols, arrow and coefficients. In chemical reactions, reactants are written at left side of arrow and products are written at right side of arrow. Number of moles of reactants and products give us coefficient in the chemical reactions. Physical states of matters are also shown in the chemical reactions in brackets like "s" for solids, "g" for gases, "l" for liquids and "aq" for matters in solutions.
Constant Values in Chemical Reactions
- Mass is always conserved in chemical reactions. In other words, total mass of reactants is equal to total mass of products.
- Number of atoms and kinds of atoms are conserved
- Structure of nuclei is conserved
- Total numbers of protons, neutrons and electrons are conserved
- In ionic chemical reactions, total charge is conserved
Variables in Chemical Reactions
- Numbers and structure of electrons in atoms can change
- Volumes and radii of atoms can change
- Chemical bonds can change
- Total volume, number of moles and molecules can not be conserved
- Physical and chemical properties of matters change
1) Combustion/Burning Reactions:
Reaction of some combustible matters with oxidizing elements like oxygen is called combustion reactions.After these reactions oxidized products are produced. In general, these reactions are exothermic.
2) Combination/Synthesis Reactions:
More than one matters combine and form new matter is called combination or synthesis reactions.
X + Y → XY
3) Decompositions/Analysis Reactions:
These reactions are opposite of combination reactions. One compound breaks down to other compounds or elements in decomposition reactions. For example;
XY → X + Y
4. Displacement/Replacement Reactions:
An element reacts with compound and replace with an element of that compound. For example;
Mg(s) + Cu(NO3)2(aq) → Mg(NO3)2(aq) + Cu(s)
5. Acid and Base Reactions (Neutralization Reactions):
Acidic and basic matters react with and we call these reactions neutralization reactions.
Acid + Base → Salt +Water
Acid + Base → Salt
6. Metal + Acid Reactions:
When metals react with acids, salt and hydrogen are produced.
Metal + Acid → Salt + H2(g)
Mg + 2HCl → MgCl2 + H2(g)
7. Metal + Base Reactions:
Since metals have base property, they do not react with bases. However, there are some exceptions like Zn and Al.
Al + 3KOH → K3AlO3 + 3/2H2(g)
8. Exothermic and Endothermic Reactions:
Reactions releasing heat are called exothermic reactions and reactions absorbing heat are called endothermic reactions.
2H2(g) + O2(g) → 2H2O + 68 kcal Exothermic Reaction
2NH3(g) + 22kcal → N2(g) + 3H2(g) Endothermic Reaction
If there is an electron transfer between matters, these reactions are called oxidation reduction or redox reactions. If atom/compound or element accept electron this process is called reduction, on the contrary, if atom/compound or element donate electron this process is called oxidation.
Conservation of Mass Theorem:
In a chemical reaction, mass is conserved, it is not lost or created. Thus;
- Number of atoms of elements are conserved. In other words, sum of the atoms in reactants part is equal to sum of the atoms of products.
- Mass of elements is conserved. Masses of reactants are equal to masses of products.
- Charges of elements/compounds are conserved. Total charges of reactants are equal to total charges of products.
- In a chemical reaction, number of molecules is not conserved always.
In balancing redox reactions, you should balance number of atoms and charges of matters in reaction.
Empirical and Molecular Formula:
Molecular formula is real formula, and it shows how many moles of atoms exist in one mole of compound. For example, C6H12O6 is real formula of glucose. 1 mole glucose includes 6 moles C atoms, 12 moles H atoms and 6 moles O atoms. On the contrary, empirical formula is the simplified form of molecular formula and it shows ratio between atoms of compound. For example, empirical formula of glucose is CH2O. Empirical formula does not give us as much information as molecular formula. More over, it can belong to more than one compound, such as CH2 is empirical formula of C2H4, C3H6, C4H8. Relation between molecular formula and empirical formula is;
(Molecular Formula)=n(Empirical Formula)
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