This is an acid-base reaction (neutralization): H2SO4 is an acid, Mg(OH)2 is a base.
Reactants:
H2SO4 – Sulfuric acid
Other names: Oil of vitriol, Sulfuric acid, concentrated (> 51% and < 100%), H2SO4Sulphuric acid, Battery acid, Hydrogen sulfate, [SO2(OH)2], [S(OH)2O2], Sulfuric acid (aqueous)
Appearance: Clear, colorless liquid ; Odourless colourless oily hygroscopic liquid ; Colorless to dark-brown, oily, odorless liquid. [Note: Pure compound is a solid below 51°F. Often used in an aqueous solution.]
Mg(OH)2 – Magnesium hydroxide
Other names: Magnesium dihydroxide, Milk of magnesia, Magnesia, [Milk of]Mg(OH)2, Magnesium hydrate
Appearance: White solid
Products:
H2O – Water, oxidane
Other names: Water (H2O), Hydrogen hydroxide (HH or HOH), Hydrogen oxideDihydrogen monoxide (DHMO) (systematic name), Hydrogen monoxide, Dihydrogen oxide, Hydric acid, Hydrohydroxic acid, Hydroxic acid, Hydrol, Μ-oxido dihydrogen, Κ1-hydroxyl hydrogen(0)
Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas
MgSO4 – Magnesium sulfate
Other names: Epsom salt (heptahydrate), English salt, Bitter saltsBath salts, MgSO4, Magnesium sulphate, Magnesium sulfate anhydrous, Epsom salt, Heptahydrate, Magnesium(II) sulfate, Magnesium sulfate (1:1), Magnesiumsulfat
Appearance: White crystalline solid ; Hygroscopic odourless white crystals or powder