Cr + 2HCl → CrCl2 + H2
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Word Equation
Chromium + Hydrogen Chloride = Chromous Chloride + Dihydrogen
One mole of
and two moles of
react to tát form one mole of
and one mole of
Thermodynamics
Thermodynamics of the reaction can be calculated using a lookup table.
Is the Reaction Exothermic or Endothermic?
| Cr (g) | 1 mol | 397.48 kJ/mol | -397.48 kJ |
|---|---|---|---|
| HCl (g) | 2 mol | -92.29904 kJ/mol | 184.59808 kJ |
| CrCl2 (s) | 1 mol | -395.388 kJ/mol | -395.388 kJ |
| H2 (g) | 1 mol | 0 kJ/mol | 0 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 mol | 174.22176 J/(mol K) | -174.22176 J/K |
|---|---|---|---|
| HCl (g) | 2 mol | 186.77376 J/(mol K) | -373.54752 J/K |
| CrCl2 (s) | 1 mol | 115.31104 J/(mol K) | 115.31104 J/K |
| H2 (g) | 1 mol | 130.586824 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 mol | 352.58568 kJ/mol | -352.58568 kJ |
|---|---|---|---|
| HCl (g) | 2 mol | -95.31152 kJ/mol | 190.62304 kJ |
| CrCl2 (s) | 1 mol | -356.0584 kJ/mol | -356.0584 kJ |
| H2 (g) | 1 mol | 0 kJ/mol | 0 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)
Instructions
To balance a chemical equation, enter an equation of a chemical reaction and press the Balance button. The balanced equation will appear above.
- Use uppercase for the first character in the element and lowercase for the second character. Examples: Fe, Au, Co, Br, C, O, N, F.
- Ionic charges are not yet supported and will be ignored.
- Replace immutable groups in compounds to tát avoid ambiguity. For example, C6H5C2H5 + O2 = C6H5OH + CO2 + H2O will not be balanced, but XC2H5 + O2 = XOH + CO2 + H2O will.
- Compound states [like (s) (aq) or (g)] are not required.
- You can use parenthesis () or brackets [].
How To Balance Equations
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Balance Cr + HCl = CrCl2 + H2 Using the Algebraic Method
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.
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
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
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)
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 Cr 1 1 ✔️ H 2 2 ✔️ Cl 2 2 ✔️ 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) | ||||||
|---|---|---|---|---|---|---|---|
| Reactants | Products | ||||||
| Cr | HCl | Total | CrCl2 | H2 | Total | ||
| Cr | 1 | 1 | 1 | 1 | ✔️ | ||
| H | 1 | 1 | 2 | 2 | ❌ | ||
| Cl | 1 | 1 | 2 | 2 | ❌ | ||
2. Multiply coefficients for compounds to tát balance out each element
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
Reactants Products Cr 1 1 ✔️ H 2 2 ✔️ Cl 2 2 ✔️
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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