Speed and velocity is a scalar and vector quantity of a similar parameter, respectively. They both refer to how fast an object moves. However, the speed only has to do with the magnitude. The velocity takes into account the sign which indicates the direction of the movement. For example, the value is -5 m/s. The speed is 5 m/s, but the velocity is 5 m/s moving downwards because the negative sign denotes downward movement or movement to the left.
So the equation is balanced, meaning they have the smallest amounts of each element in the reactants to create the products.
So, 2 moles of H2S (the coefficient) contributes to 2 moles Ag2S, which is why the ratio is 2:2.
I hope that made sense.
The liquid will stop converting into vapor. This process is to balanced the amount of substance of both phases inside the flask.
Plant: leaf tissue
Human: lungs