Respuesta :

Answer:

It's from the quation:

[tex] \boxed{ \mathsf{ \underline{2K} +\underline{2 H_2O} \rightarrow \:\underline{2}KOH + H_2 }}[/tex]

(How did I know?)

I learnt it while studying the elements of group 1.

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Group 1 elements:

K, here, is Potassium. It's position in the periodic table is Group 1, Period 4.

  • Group 1 elements are also called Alkali metals.

  • Group 1 elements have 1 electron in their valence shell(outermost shell), the electron that takes part in chemical reactions.

Valance electrons of elements of this group contribute to the valency of the group's elements I.e.,

valency of Alkali metals is 1!

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Reaction with water:

  • Alkali metals react vigorously with cold water to form their hydroxides alongwith the evolution of Hydrogen gas.

What are hydroxides?

Hydroxides of an element comprises one atom each of oxygen and Hydrogen bonded together, acting as an anion, the hydorxide anion — OH-.

Example:

  • KOH (hydroxide of Potassium)
  • NaOH (Hydroxide of Sodium)

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Back to the question:

In the question, The reactants are missing but the products are known, that are, Potassium Hydroxide and water.

Keeping the above mentioned property in mind, the reactants come clear as Potassium(K) and Cold water(H2O).

that makes the equation:

[tex] \mathsf{K + H_2O \rightarrow \: KOH + H_2 }[/tex]

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Balancing the equation:

For an equation to be balanced, the number of atoms of each elements on both side of the equation must be equal.

Number of atoms of each element on the LHS:

  • K = 1
  • H = 2
  • O = 1

(subscript in front of an atom represents its number of atoms in the compund)

Number of atoms of each element on the LHS:

  • K = 1
  • H = 1 + 2 = 3
  • O = 1

The number of Hydrogen atoms on boths sides is NOT balanced!

Hit and trial method:

If we add a "2" in front of K, H2O and KOH

[tex] \mathsf{ \underline{2K} +\underline{2 H_2O} \rightarrow \:\underline{2}KOH + H_2 }[/tex]

Number of atoms on both the sides become equal.

(TIP: This comes thru practice:/. but main point is even out the oxygen and Hydrogen atoms first. like if it's 3 multiply it by 2 and you get an even number, I.e., 6)

Number of atoms of each element on the LHS:

  • K = 2
  • H = 4
  • O = 2

Number of atoms of each element on the LHS:

  • K = 2
  • H = 2 + 2 = 4
  • O = 2

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Answer:

Hence, the balanced form of the equation is:

[tex] \boxed{ \mathsf{ \underline{2K} +\underline{2 H_2O} \rightarrow \:\underline{2}KOH + H_2 }}[/tex]

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