Content code
c1049
Slug (identifier)
the-main-formulas-used-in-chemistry
Parent content
Generalities in Chemistry
Grades
Secondary V
Topic
Chemistry
Tags
formulas in chemistry
molar concentration
ideal gas law
calorimetry
acidity
Dalton's Law
Kps
Content
Contenu
Links
Type
Anchor
Title
General formulas
Anchor
general-formulas
Type
Anchor
Title
Gas laws
Anchor
gas-laws
Type
Anchor
Title
The energy aspect of transformations
Anchor
the-energy-aspect-of-transformations
Type
Anchor
Title
Reaction speed
Anchor
reaction-speed
Type
Anchor
Title
Chemical balance
Anchor
chemical-balance
Title (level 2)
General formulas
Title slug (identifier)
general-formulas
Contenu
Corps

The number of moles (|n|)

 ||n=\frac{m}{M}||
 

The number of moles (|n|) is equal to the ratio of the experimental mass (|m|) to the molar mass (|M|).

 

|n|: number of moles |\text{(mol)}|

|m|: mass |\text{(g)}|

|M|: molar mass |\text{(g/mol)}|

 

Molar concentration (or molarity) (|C|)

 ||C=\frac{n}{V}||
 

The molarity (|C|) is the number of moles (|n|) of solute for a total volume (|V|) of |text{1 L}| of solution.

 

|n|: number of moles |\text{(mol)}|

|V|: volume of solution |\text{(L)}|

|C|: molar concentration |\text{(mol/L)}|

 

Concentration and volume before and after dilution

 ||C_{1}\cdot V_{1}=C_{2}\cdot V_{2}||
 

The product of the initial volume (|V_{1}|) and the initial concentration (|C_{1}|) is equal to the product of the final volume (|V_{2}|) and the final concentration (|C_{2}|).


It is important to use the same units of volume and concentration for the initial and final situations.


|C_{1}|: initial concentration

|V_{1}|: initial volume

|C_{2}|: final concentration

|V_{2}|: final volume

 

The transformation of degrees Celsius |\text{(°C)}| into kelvins |\text{(K)}| or vice versa
 

|T\ (^\circ C)+273,15=T\ (K)|

 

|T\ (K)-273,15=T\ (^\circ C)|

 

The acidity of a solution
 

||pH=-log\;[H^{+}]||

 

 

||pH=log\;\frac{1}{[H^{+}]}||

 


||pH+pOH=14||

 
 |[H^+]| represents the concentration of |H^+|

The concentration of |H^+| and |OH^-| ions in a neutralisation reaction

 ||V_{a}\cdot[H^{+}]=V_{b}\cdot[OH^{-}]|| The product of the acidic volume and the |H^+| concentration is equal to the product of the basic volume and the |OH^-| concentration.
Title (level 2)
Gas laws
Title slug (identifier)
gas-laws
Contenu
Corps

The law of perfect gases

 ||PV=nR​T||
|R|: perfect gas constant |(8,314 \  \text{kPa} \cdot \text{L/(mol} \cdot \text{K)})|
|V|: volume |\text{(L)}|
|P|:pressure |\text{(kPa)}|
|n|: ​quantity of gas |\text{(mol)}|
|T|: temperature |\text{(K)}|

The general law of gases

 ||\frac{P_{1}\cdot V_{1}}{n_{1}\cdot T_{1}}=R=\frac{P_{2}\cdot V_{2}}{n_{2}\cdot T_{2}}||
This law is useful when conditions vary, whether in terms of volume |(V)|, pressure |(P)|, number of moles |(n)| or temperature |(T)|.
|V|: volume |\text{(L)}|
|P|: pressure |\text{(kPa)}|
|n|: quantity of gas |\text{(mol)}|
|T|: temperature |\text{(K)}|
This law brings together all the other gas laws: Avogadro, Charles, Boyle-Mariotte and Gay-Lussac.
 

Dalton's Law

 ||P_{totale}=P_{p1}+P_{p2}+P_{p3}+...|| This law is used to express the total pressure exerted by the partial pressures of the gases in a mixture.

The partial pressure of a gas
||P_{pA}= P_{T}\frac{n_{A}}{n_{T}}||
|P_{pA}|: partial pressure of gas A |\text{(kPa)}|
|P_{T}|: total pressure of the mixture |\text{(kPa)}|
|n_{A}|: quantity of gas A |\text{(mol)}|
|n_{T}|: total quantity of gas |\text{(mol)}|

Graham's Law

 ||\frac{v_{1}}{v_{2}}=\sqrt{\frac{M_{2}}{M_{1}}}||
This law states that when two gases diffuse in the same medium, the ratio between their velocities is inversely proportional to the square root of their molar mass or density.
 
|v_{1}|: gas diffusion speed 1 |\text{(m/s)}|
|v_{2}|: gas diffusion speed 2 |\text{(m/s)}|
|M_{1}|: molar mass of gas 1 |\text{(g/mol)}|
|M_{2}|: molar mass of gas 2 |\text{(g/mol)}|
Title (level 2)
The energy aspect of transformations
Title slug (identifier)
the-energy-aspect-of-transformations
Contenu
Corps

Calorimetry

 		 ||Q=m\cdot​ c\cdot\Delta T||

|Q|: amount of energy transferred |\text{(J)}|

|m|: mass of the substance undergoing the temperature change |\text{(g)}|

|c|: heat capacity of the substance |\text{(J/(g.°C))}|

|\Delta T|: temperature variation |\text{(°C)}|

Energy transfer for the same substance

 ||(m_{1}\cdot T_{1})+(m_{2}\cdot T_{2})=(m_{tot}\cdot T_{f})||
This relationship is used to transfer energy for the same substance with different mass quantities (or volumes) and temperatures.
 
Indices 1 are associated with a substance (e.g. one with a high temperature). Subscripts 2 are associated with a second substance (for example, one with a low temperature).
 
|m_{tot}|: total mass of the two substances
|T_{f}|: final temperature between the two substances

The molar heat of reaction (|Delta H|)

 ||\Delta H=\frac{Q}{n}||
The heat quantity |(Q)| is reduced to 1 mole and the appropriate sign convention is applied:
positive (+) if the reaction is endothermic and negative (-) if the reaction is exothermic.

The variation in enthalpy

 ||\Delta H=H_{p}-H_{r}||
|\Delta H|:enthalpy variation (in J)
|H_{p}|: enthalpy of products (in J)
|H_{r}|: enthalpy of reactants (in J)

Hess's law

||\Delta H_{tot}=\Delta H_{1}+\Delta H_{2}+\Delta H_{3}+...||

 The enthalpy variation (|Delta H|) of an overall reaction is equal to the sum of the |Delta H| of the individual stages.

Here are different ways to find the ΔH:

1. The sum of the enthalpies of the products and reactants can be compared.
||\Delta H=(\Sigma H_{p}-\Sigma H_{r})||

2. The values of the direct and inverse activation energies can be compared.
||\Delta H=(E_{a\; directe})-(E_{a\; inverse})||

3. We can compare the energies when links are broken and when links are formed.
||\Delta H=E_{tot.\; absorb\acute{e}e}-E_{tot.\; d\acute{e}gag\acute{e}e}||
Title (level 2)
Reaction speed
Title slug (identifier)
reaction-speed
Contenu
Corps

Measuring the speed of a reaction

||Speed; of; r\acute{e} action=frac{Measure; of; change}{unitacute{e}; of; time}||

||Speed; amount; reaction=frac{Decrease; amount; reactants}{unit; amount; time}||

||Speed; time; action=frac{Increase; quantity; products}{unit; time}||

The law of the speed of a reaction (law of mass action or Guldberg and Waage's laws)

||v=k[A]^{x}[B]^{y}||

 


||xA+yB\rightarrow zC||

The rate of a reaction at a given temperature is directly proportional to the product of the concentration of the reactants raised to the power corresponding to their respective coefficient in thebalanced equation.

Thus, in the following hypothetical example

2 A (g) + B (g) →A2B (g), we would have:

v = k [A]2 [B].

The general rate of reaction

||aA+bB\rightarrow cC+dD||


|v=\frac{-1}{a}\frac{\Delta[A]}{\Delta t}=\frac{-1}{b}\frac{\Delta[B]}{\Delta t}=\frac{1}{c}\frac{\Delta[C]}{\Delta t}=\frac{1}{d}\frac{\Delta[D]}{\Delta t}|

|v|: general velocity (in |mol/L\cdot s|)
|a|,|b|,|c| and |d|: coefficients for each substance
|\Delta[A]|,|\Delta[B]|,|\Delta[C]| and |\Delta[D]|: variations in the concentration of each substance involved in the reaction (in |mol/L|)
|Delta t|: variation in time (in |s|)
Title (level 2)
Chemical balance
Title slug (identifier)
chemical-balance
Contenu
Corps
The acidity constant  

||K_{a}=\frac{[H^{+}][A^{-}]}{[HA]}||

 

||HA_{(aq)}\rightleftharpoons H_{(aq)}^{+}+A_{(aq)}^{-}||
|K_{a}|: acidity constant
|[H^{+}]|: concentration of hydronium ions in water (in mol/L)
|[A^{-}]|: concentration of conjugate base (in mol/L)
|[HA]|: concentration of undissociated acid (in mol/L)

The basicity constant

||K_{b}=\frac{[B^{+}][OH^{-}]}{[B]}||

 

||B_{(aq)}+H_{2}O_{(l)}\rightleftharpoons B_{(aq)}^{+}+OH_{(aq)}^{-}||
|K_{b}|: basicity constant
|[B^{+}]|: concentration of conjugated acid (in mol/L)
|[OH^{-}]|: concentration of |OH^{-}| ions in water (in mol/L)
|[B]|: concentration of untransformed base (in mol/L)

Calculating the value of the equilibrium constant (KC or Ké)

||K_{c}=\frac{[C]^{c}\cdot[D]^{d}}{[A]^{a}\cdot[B]^{b}}||

 

 

||aA+bB\rightarrow cC+dD||

 In these calculations, only gases and ions are involved. Reactants and products in solid and liquid form should not be considered.

The solubility product constant

||K_{ps}=[X^{+}]^{n}[Y^{-}]^{m}||

 


||X_{n}Y_{m(s)}\rightleftharpoons nX_{(aq)}^{+}+mY_{(aq)}^{-}||

 
|K_{ps}|: solubility product constant
|[X^{+}]| and |[Y^{-}]|: equilibrium ion concentrations (in mol/L)
n and m: coefficients for each ion

In an acid-base environment, it is useful to remember the ionisation constant of water (KH2O).

 ||K_{H_{2}O}=[H^{+}]\cdot[OH^{-}]=1\times10^{-14}\grave{a}\;25^{o}C||
Remove audio playback
No
Printable tool
Off