cr + hcl

Cr + 2HClCrCl2 + H2

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Word Equation

Chromium + Hydrogen Chloride = Chromous Chloride + Dihydrogen

One mole of

Chromium [Cr]

and two moles of

Hydrogen Chloride [HCl]

react to tát form one mole of

Chromous Chloride [CrCl2]

and one mole of

Dihydrogen [H2]


Thermodynamics of the reaction can be calculated using a lookup table.

Is the Reaction Exothermic or Endothermic?

Cr (g)1 mol397.48 kJ/mol-397.48 kJ
HCl (g)2 mol-92.29904 kJ/mol184.59808 kJ
CrCl2 (s)1 mol-395.388 kJ/mol-395.388 kJ
H2 (g)1 mol0 kJ/mol0 kJ
ΣΔH°f(reactants)212.88192 kJ
ΣΔH°f(products)-395.388 kJ
ΔH°rxn-608.26992 kJ

ΣΔH°f(reactants) > ΣΔH°f(products), so sánh Cr + HCl = CrCl2 + H2 is exothermic (releases heat).

Is the Reaction Exoentropic or Endoentropic?

ΔS = Sproducts - Sreactants. If ΔS < 0, it is exoentropic. If ΔS > 0, it is endoentropic.

Cr (g)1 mol174.22176 J/(mol K)-174.22176 J/K
HCl (g)2 mol186.77376 J/(mol K)-373.54752 J/K
CrCl2 (s)1 mol115.31104 J/(mol K)115.31104 J/K
H2 (g)1 mol130.586824 J/(mol K)130.586824 J/K
ΣΔS°(reactants)547.76928 J/K
ΣΔS°(products)245.897864 J/K
ΔS°rxn-301.871416 J/K

ΣΔS°(reactants) > ΣΔS°(products), so sánh Cr + HCl = CrCl2 + H2 is exoentropic (decrease in entropy).

Is the Reaction Exergonic or Endergonic?

ΔG = Gproducts - Greactants. If ΔG < 0, it is exergonic. If ΔG > 0, it is endergonic.

Cr (g)1 mol352.58568 kJ/mol-352.58568 kJ
HCl (g)2 mol-95.31152 kJ/mol190.62304 kJ
CrCl2 (s)1 mol-356.0584 kJ/mol-356.0584 kJ
H2 (g)1 mol0 kJ/mol0 kJ
ΣΔG°(reactants)161.96264 kJ
ΣΔG°(products)-356.0584 kJ
ΔG°rxn-518.02104 kJ

ΣΔG°(reactants) > ΣΔG°(products), so sánh Cr + HCl = CrCl2 + H2 is exergonic (releases energy).

Reaction Expressions

Kc or Q = ( [CrCl2] [H2] ) / ( [Cr] [HCl]2 )

(assuming all reactants and products are aqueous. substitutue 1 for any solids/liquids, and Psubstance for gases.)

rate = -(Δ[Cr] / Δt) = -1/2 * (Δ[HCl] / Δt) = (Δ[CrCl2] / Δt) = (Δ[H2] / Δt)

(assuming constant volume in a closed system and no accumulation of intermediates or side products)


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Balance Cr + HCl = CrCl2 + H2 Using the Algebraic Method

How To Balance Cr + HCl = CrCl2 + H2

To balance the equation Cr + HCl = CrCl2 + H2 using the algebraic method step-by-step, you must have experience solving systems of linear equations. The most common methods are substitution/elimination and linear algebra, but any similar method will work.

  1. Label Each Compound With a Variable

    Label each compound (reactant or product) in the equation with a variable to tát represent the unknown coefficients.

    a Cr + b HCl = c CrCl2 + d H2

  2. Create a System of Equations

    Create an equation for each element (Cr, H, Cl) where each term represents the number of atoms of the element in each reactant or product.

    Cr: 1a + 0b = 1c + 0d H: 0a + 1b = 0c + 2d Cl: 0a + 1b = 2c + 0d

  3. Solve For All Variables

    Use substitution, Gaussian elimination, or a calculator to tát solve for each variable.

    • 1a - 1c = 0
    • 1b - 2d = 0
    • 1b - 2c = 0

    Use your graphing calculator's rref() function (or an online rref calculator) to tát convert the following matrix into reduced row-echelon-form:

    [ 1 0 -1 0 0] [ 0 1 0 -2 0] [ 0 1 -2 0 0]

    The resulting matrix can be used to tát determine the coefficients. In the case of a single solution, the last column of the matrix will contain the coefficients.

    Simplify the result to tát get the lowest, whole integer values.

    • a = 1 (Cr)
    • b = 2 (HCl)
    • c = 1 (CrCl2)
    • d = 1 (H2)
  4. Substitute Coefficients and Verify Result

    Count the number of atoms of each element on each side of the equation and verify that all elements and electrons (if there are charges/ions) are balanced.

    Cr + 2 HCl = CrCl2 + H2

    Reactants Products

    Since there is an equal number of each element in the reactants and products of Cr + 2HCl = CrCl2 + H2, the equation is balanced.

Balance Cr + HCl = CrCl2 + H2 Using Inspection

The law of conservation of mass says that matter cannot be created or destroyed, which means there must be the same number atoms at the kết thúc of a chemical reaction as at the beginning. To be balanced, every element in Cr + HCl = CrCl2 + H2 must have the same number of atoms on each side of the equation. When using the inspection method (also known as the trial-and-error method), this principle is used to tát balance the one element at a time until both sides are equal and the chemical equation is balanced.

1. Count the number of each element on the left and right hand sides

Reactants (Left Hand Side)Products (Right Hand Side)

2. Multiply coefficients for compounds to tát balance out each element

  1. H is not balanced. Add 1 molecule(s) of HCl to tát the reactant (left-hand) side to tát balance Hydrogen: Cr + 2HCl = CrCl2 + H2


3. Verify that the equation is balanced

Since there are an equal number of atoms of each element on both sides, the equation is balanced.

Cr + 2HCl = CrCl2 + H2

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