Complete and balance each gas-evolution equation. a. HBr(aq) + NiS(s) → d. HClO₄(aq) + Li₂CO₃(aq) →

Verified step by step guidance

1. Step 1: Identify the reactants and products for each reaction. For reaction (a), the reactants are HBr(aq) and NiS(s). For reaction (d), the reactants are HClO_4(aq) and Li_2CO_3(aq).
2. Step 2: Determine the type of reaction. Both reactions are gas-evolution reactions, which typically involve the formation of a gas as one of the products.
3. Step 3: Predict the products. For reaction (a), HBr reacts with NiS to form H_2S(g) and NiBr_2(aq). For reaction (d), HClO_4 reacts with Li_2CO_3 to form CO_2(g), H_2O(l), and LiClO_4(aq).
4. Step 4: Write the unbalanced chemical equations. For reaction (a), it is HBr(aq) + NiS(s) → H_2S(g) + NiBr_2(aq). For reaction (d), it is HClO_4(aq) + Li_2CO_3(aq) → CO_2(g) + H_2O(l) + LiClO_4(aq).
5. Step 5: Balance each equation by adjusting coefficients to ensure the same number of each type of atom on both sides of the equation. Start with the most complex molecule and balance elements one at a time, checking each element as you proceed.