Answer:
Double Replacement
Explanation:
Let's consider the following balanced reaction that occurs between aluminum sulfate and tripotassium phosphate.
Al₂(SO₄)₃ + 2 K₃PO₄ ⇒ 2 AlPO₄ + 3 K₂SO₄
This is a double replacement reaction because both salts exchange their cations and anions. So, PO₄³⁻ takes the place of SO₄²⁻ in Al₂(SO₄)₃ and SO₄²⁻ takes the place of PO₄³⁻ in K₃PO₄.
The internal energy has the symbol U. Q is positive if heat is added to the system, and negative if heat is removed;
....."W is positive if work is done by the system"........
and negative if work is done on the system.
So, work done by a system is positive.
