Answer:
 ⇒  
Explanation:
In balancing a chemical equation we make sure the number of atoms of each element on the reactant side of the equation equals that on the product side
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The equation above represents an unbalanced equation of the reaction of aqueous ammonium chloride  with aqueous barium nitrate .we can balance this equation by adding the right coefficients to reactants and product.
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HA ⇄ H⁺ + A⁻ 
so:
![\frac{[H^+][A^-]}{[HA]} = 1.5 x 10^{-5}](https://tex.z-dn.net/?f=%20%5Cfrac%7B%5BH%5E%2B%5D%5BA%5E-%5D%7D%7B%5BHA%5D%7D%20%3D%201.5%20x%2010%5E%7B-5%7D%20%20)
and now:

 = 1.5 x 10⁻⁵
x is considered very small compared to 0.15
x² = 2.25 x 10⁻⁶
x = 1.5 x 10⁻³
So [H⁺] = 1.5 x 10⁻³
pH = - log [H⁺] = - log (1.5 x 10⁻³) = 2.83
 
        
             
        
        
        
I think because each element has its own number of protons and neutrons, giving it its own atomic number and mass (correct me if I’m wrong please)
        
             
        
        
        
Answer:
 0°C.
Explanation:
Hello,
In this case, given the heating curve of water on the attached document, we can notice that at 0 °C the solid starts melting, which means that the melting point is reached. Melting point is known as a physical change whereby a solid changes to liquid by the addition of heat as it allows the molecules to separate to each other. 
Best regards.
 
        
             
        
        
        
Answer: heat 
Other indicators: color change, odor, gas, temperature change.