Because the number of valence electrons of an element determines the properties and in particular the reactivity of that element.
In fact, elements of the first group (i.e. only one valence electron) have high reactivity, because they can easily give away their valence electron to atoms of other elements forming bonds. On the contrary, elements of the 8th group (noble gases) have their outermost shell completely filled with electrons, so they do not have valence electrons, and they have little or no reactivity at all.
Well, you would reply that that's not what theories are. Theories explain the how and the why, laws explain the what. So, the Big Bang theory isn't "just a theory". It's a theory, it explains the how. (Also, if someone tells you it's anti-God or whatever, tell them the thoery was created by a Catholic scientist. True fact.) I hoped this helped!!! (You don't have the include who created the theory if this is for homework.)
A. through a relatively short distance.
The speed is actually called the drift speed of the electron.
Answer:
A,B,D,E are wrong
(A) Heat exchangers are devices where two moving fluid streams are mixed together (B) Heat exchangers are devices where two moving fluid streams exchange mass (D) Heat exchangers are devices where two moving fluid streams exchange mechanical work without mixing together (E) There is no heat transfer between the two fluids of an insulated heat exchanger
Explanation:
A heat exchanger can be regarded as a system that bring about transfer heat between two or more than two fluids. It can function in cooling process and heating processes, the fluids involves in this process can have a solid wall to separate them so as to prevent mixing, direct contact could also be utilized. The mechanism is making hot gas jets which could fire upward over a glowing water that is passing through pipes, as water moves along the pipe, heat energy is been absorbed and there is heating up i.e heat is transferred. One is cooked the other is heated up. It is very essential to insulate the whole steam system along with heat exchangers so that energy could be saved and the temperature of the surface would be at safe-to-touch range and also steam quality could be maintained. The types of heat exchanger we have are;
✓Shell and tube heat exchangers.
✓Condensers, evaporators, and boilers
✓Double pipe heat exchangers.
✓Plate heat exchangers.
It should be noted Heat exchangers are devices where two moving fluid streams exchange heat (thermal energy) without mixing together
