Can someone please help me im stuck​

The answers to your questions are given below.

Explanation:

1. __H₂ + __O₂ —> __H₂O

The above equation can be balance as follow:

H₂ + O₂ —> H₂O

There are 2 atoms of O on the left side and 1 atom on the right side. It can be balance by writing 2 before H₂O as shown below:

H₂ + O₂ —> 2H₂O

There are 2 atoms of H on the left side and a total of 4 atoms on the right side. It can be balance by writing 2 before H₂ as shown below:

2H₂ + O₂ —> 2H₂O

Now the equation is balanced.

Elements >>> Reactants >>> Products

H >>>>>>>>> 4 >>>>>>>>>>> 4

O >>>>>>>>> 2 >>>>>>>>>>> 2

2. __ P₄ + __O₂ —> __P₂O₃

The above equation can be balance as follow:

P₄ + O₂ —> P₂O₃

There are 4 atoms of P on the left side and 2 atoms on the right side. It can be balance by writing 2 before P₂O₃ as shown below:

P₄ + O₂ —> 2P₂O₃

There are 2 atoms of O on the left side and a total of 6 atoms on the right side. It can be balance by writing 3 before O₂ as shown below:

P₄ + 3O₂ —> 2P₂O₃

Now, the equation is balanced

Elements >>> Reactants >>> Products

P >>>>>>>>> 4 >>>>>>>>>>> 4

O >>>>>>>>> 6 >>>>>>>>>>> 6

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.