This is a great question! The answer to it lies in the fact that Venus has a very dense atmosphere made up of carbon dioxide, nitrogen, and sulfuric acid, while Mercury has a very thin atmosphere with various gases, but very little carbon dioxide. So what's so important about carbon dioxide? Well, sunlight will pass through Venus' clouds (which contain mostly carbon dioxide) and warm the surface of the planet. Usually, the surface of a planet is warmed during the day and cools off at night by releasing infrared radiation (heat) back into space. But the carbon dioxide in Venus' clouds absorbs energy from infrared radiation very well and "traps" the heat on the planet, making it very warm. This has sometimes been called a "runaway greenhouse effect." We don't see this happen on Mercury because its atmosphere is not thick and does not have much carbon dioxide in it. I hope this helps!

Venus is hotter than Mercury because it has a much thicker atmosphere. The atmosphere, the gaseous layer surrounding a planet, is like a blanket. Think of two people sitting next to a campfire one is much closer to the fire while another is further away. The one that is closer doesn't have a blanket (Mercury), while the other further away has a sleeping bag (Venus). Both persons are getting heat from the fire but the person with the sleeping bag keeps all the heat he or she gets. Mercury is closer but because it has a very thin or no atmosphere at all the heat goes out into space. Venus on the other hand with it's much thicker atmosphere holds all the heat it gets. The heat the atmosphere traps is called the greenhouse effect. If Venus did not have an atmosphere the surface would be -128 degrees Fahrenheit much colder than 333 degrees Fahrenheit, the average temperature of Mercury.

Venus is hotter due to the greenhouse effect: Venus has an atmosphere about ninety times thicker than that of Earth, and made almost entirely of carbon dioxide, which is one of the gasses that causes the greenhouse effect on Earth. The greenhouse effect on Venus is so great that it raises the surface temperature on Venus to, as you say, hotter than that of Mercury, despite being farther from the sun.