When you heat up most substances it gives them more Kinetic energy and the substance becomes less arranged in an ordered state, further apart and move faster. therefore the answer is the first: They gain a higher average kinetic energy
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Hey there!
Great question;)
Answer:Physical change
Explanation: When sugar mixes with water, at the end, the chemical formulas are the same. Nothing has changed!
I hope this helps;)
Answer : The internal energy change is, -506.3 kJ/mol
Explanation :
Formula used :

or,

where,
= change in enthalpy = 
= change in internal energy = ?
= change in moles
Change in moles = Number of moles of product side - Number of moles of reactant side
According to the reaction:
Change in moles = 0 - 2 = -2 mole
That means, value of
= 0
R = gas constant = 8.314 J/mol.K
T = temperature = 
Now put all the given values in the above formula, we get




Therefore, the internal energy change is -506.3 kJ/mol
B) The elements become less reactive.