Answer:
A well tested explanation of a natural phenomenon
Explanation:
A scientific theory is an explanation of a natural phenomenon which has been drawn from a well tested observation. 
Theories are products of repeated scientific experiments. When a hypothesis otherwise known as a "scientific guess" survives a lot of scrutiny, we can elevate it to the status of a theory. Most theories starts off from simple observations. These observations can further spark series of experiments in such a field and a scientific guess proposed. Further testing and experimenting would now lead to a theory. 
 
        
             
        
        
        
<u>Answer:</u> The  for the reaction is -1052.8 kJ.
 for the reaction is -1052.8 kJ.
<u>Explanation:</u>
Hess’s law of constant heat summation states that the amount of heat absorbed or evolved in a given chemical equation remains the same whether the process occurs in one step or several steps.
According to this law, the chemical equation is treated as ordinary algebraic expressions and can be added or subtracted to yield the required equation. This means that the enthalpy change of the overall reaction is equal to the sum of the enthalpy changes of the intermediate reactions.
The given chemical reaction follows:
 
      
The intermediate balanced chemical reaction are:
(1)  
    
(2)  
     
The expression for enthalpy of the reaction follows:
![\Delta H^o_{rxn}=[1\times \Delta H_1]+[1\times (-\Delta H_2)]](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B1%5Ctimes%20%5CDelta%20H_1%5D%2B%5B1%5Ctimes%20%28-%5CDelta%20H_2%29%5D)
Putting values in above equation, we get:

Hence, the  for the reaction is -1052.8 kJ.
 for the reaction is -1052.8 kJ.
 
        
             
        
        
        
From the information given:
- The volume of the graduated cylinder = 50.0 mL
- when a sterling silver pendant is added, the volume increases to = 61.3 mL
∴
The volume of the sterling silver pendant is:
= 61.3 mL - 50.0 mL
= 11.3 mL
Since, 1 mL = 1cm³
Then;
 11.3 mL = 11.3 cm³
- the density of the sterling silver = 10.25 g/cm³
Using the relation for Density; i.e.


mass = 10.25 g/cm³× 11.3 cm³
mass of the sterling silver = 115.825 grams
Recall that sterling silver has:
- 92.5% silver and;
- 7.5% copper
∴
The mass of the copper contained in the sterling silver pendant can be calculated as:

= 8.687 grams
Therefore, we can conclude that the mass of the copper contained in the sterling silver pendant is  8.687 grams
 Learn more about the relation between Density, Mass, and Volume here:
brainly.com/question/24386693?referrer=searchResults
 
        
             
        
        
        
Answer: 368 grams of sodium reacted.
Explanation:
The balanced reaction is :
 
 
 
    

 
    
According to stoichiometry :
2 moles of  are formed from = 2 moles of
 are formed from = 2 moles of 
Thus 16 moles of  are formed from=
 are formed from= of
  of 
Mass of 
Thus 368 grams of sodium reacted.
 
        
             
        
        
        
Is go be 4x=7 so when you see yo thing pick the 2nd one it's go be b