Answer: Energy of reactants = 30, Energy of products = 10
Exothermic
Activation energy for forward reaction is 10.
Explanation:
Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and 
for the reaction comes out to be negative.
Energy of reactants = 30
Energy of products = 10
Thus as energy of the product < energy of the reactant, the reaction is exothermic.
Activation energy 
is the extra energy that must be supplied to reactants in order to cross the energy barrier and thus convert to products.
for forward reaction is (40-30) = 10.
WOW, I gave you the answer, i used a periodic table, i got the mass of gold and i linked a helpful link my teacher gave me because we used it in a lab once.
Answer:
Nucleus
Explanation:
they originate in the nucleus
The density of water is a physical property.
You can measure it without changing the water to a different substance.
It is <em>not a physical change</em> because the water does not change to ice or steam.
You can observe a <em>chemical property</em> or a <em>chemical change</em> only if the water <em>changes to a different substance</em>.
Answer:
number of valence electrons
Explanation:
All of the elements in group 17, also known as group 7A, have 7 valence electrons.
No two elements have the same atomic number nor atomic mass in elemental form.
Halogens may have any number of isotopes.
