Is the habitable zone smaller than what it is said to be? Also the theories of why Venus is the way it is.?

It is still in the habitable zone, but you would need to terraform the planet first.

It's possible that Venus changed because its rotation was slowed by the gravitational pull of the Earth. At its closest approach to Earth, Venus presents the same face and rotates in the reverse direction to other planets apart from Uranus. This may have caused the sun to bake carbon dioxide out of carbonate rocks on the surface, causing a runaway greenhouse effect. If Earth wasn't here, Venus could well be habitable.

Yes - Venus might at one point been like Earth. But it "outgassed" - sort of "turned inside out". Earth did this too a number of times like the Deccan Traps in India (65 million years back) and the great flood of magma which came out of the earth in Washington State 13 million years ago.

The Earth has also opened up a few times and created conditions which would probably have killed all humans. But then gradually the Earth recovered from its temper tantrum. However apparently Venus never did - and the volcanic insides just kept pouring out. There's probably plenty of water on Venus, but now it's all tied up in the atmosphere.

Too bad. It would have been interesting to have another habitable planet besides Earth.

The 'habitable zone' is really an estimate of where liquid water could exist; it doesn't assume what kind of planetary conditions exist on a planet within that zone.... Much beyond Mars, we know that the sun's light couldn't carry enough energy to maintain liquid water. Closer than Venus, we know there's so much light that water couldn't be liquid there, either. But, from about the orbit of Venus to just outside the orbit of Mars, there's an area where enough heat and light could maintain liquid water on a planet's surface - **if that planet had Earth-like conditions** - such as a similar atmospheric pressure, surface gravity, and rotation.

And - it also assumes the star in question is relatively stable. Our sun is a very stable system; so, while Venus may have had liquid water at one time, what we see today probably wasn't due to changes in our sun, but more likely the addition of gases to Venus' atmosphere (probably from volcanic activity). Without oceans to dissolve the CO2 in, and without plants to trap carbon, we have the runaway greenhouse effect we see today.