Hey there!
In a single replacement reaction, one element replaces another in a compound.
Zinc and hydrogen chloride react to produce zinc chloride and hydrogen.
Zinc replaces hydrogen.
Zn + HCl → H₂ + ZnCl₂
This isn't balanced, so we should balance this.
Balance Cl: 1 on the left, 2 on the right, add a coefficient of 2 in front of HCl.
Zn + 2HCl → H₂ + ZnCl₂
Balance H: 2 on the left, 2 on the right, already balanced
Balance Zn: 1 on the left, 2 on the right, already balanced.
So, here's the equation for a single replacement reaction between zinc and hydrogen chloride:
Zn + 2HCl → H₂ + ZnCl₂
Hope this helps!