Whenever energy changes form, people sometimes say that some energy is "lost." What is meant by this?
A. The energy is not truly lost; it transforms into forms that are not easily put to use.
B. The process of changing form reduces the total amount of energy in the universe.
C. Whenever energy changes form in one location, a corresponding change in the opposite direction must take place somewhere else.
D. Sometimes a "mistake" or an inefficiency in the transformation causes energy to be destroyed.

A. The energy is not truly lost: it transforms into forms that are not easily put to use.

Explanation:

This is due to the fact that when we use energy, it seems to have disappear, but it really hasn't. In fact, when we use energy, it is changing into another form that has to be converted in order for energy to be present once again.

  1.the balanced   chemical equation is as below

cu +   2 ag(no)₃ → cu(no₃)₂   +2 ag

2.the   much silver   produced   is   50.9 g

step 1: find the   moles of cu

moles =   mass÷   molar mass

  from periodic table the molar mass of cu = 63.5 g/mol

moles is therefore = 15.00 g÷ 63.5 g/mol = 0.236   moles

step 2: use the mole ratio to determine the   moles of ag

from equation above   cu: ag   is 1: 2

therefore the moles of ag   =0.236   moles   x 2/1 =0.472   moles

step 3: find the mass   of ag

mass = moles x molar mass

from periodic table   the molar mass of ag =107.87 g/mol

mass   = 0.472   moles x 107.87 g/mol = 50.9 g

3.   the   much   silver   collected worth is   1.797 oz

  convert   50.9 g   to oz

that is   1 gram = 0.0353 oz

          50.9 grams =?   oz

by cross multiplication

={(50.9 grams x 0.0353 oz) / 1   gram}   =1.797 oz