How much TNT would it take to blow up an ordinary suburban house? Also, can you make TNT or any similar high explosive from the ingredients found in a typical kid's chemistry set? This is for a story about some teenagers in the 70s, aiming to create a science fair experiment that you can bet is going to go horribly wrong.
Define "blow up": combat engineers do not blow up bridges - they drop them, because "blowing up" anything is a waste of explosives.
What is the construction of the house and what damage do you want to do? Make the interior uninhabitable or scatter it over a quarter mile radius?
You will not get anything remotely explosive in a kids' chemistry set - the health and safety police will not allow it. If you want to go down the "blow something up" route, the use of a propane/butane with air mix will give you sufficient explosive power with easily available materials.
The synthesis of high or powerful explosives involves the use of chemicals that you would keep children tens of meters away from.
Propane driven bunsen burner in chemistry set. Leak.........
Everything is on the internet these days, but I'd think twice about putting a genuine bomb recipe into a short story. Some fool kid might try it. You might not be legally responsible, but morally you are. The fewer details, the better.
That being said, cooking up TNT is not the way to go about it. There are other explosives which are less safe and less powerful, but quantity can substitute for quality. For an accident, consider a dust explosion. Or perhaps electrolysis, from an electroplating demonstration gone wrong.
Follow-Up: Back in school, the teacher took a little metal box with a lid and a tiny hole, put a drop of gasoline into it, and shook it. Then he applied a match to the hole. Result, a bang and the lid flew off. Quite a lot of flammable things become explosive when they are finely dispensed. Fuel, coal dust, etc. The same effect as the gas leak suggested by RoyC.
As your goal is a science fair experiment, I'm just going ahead and not use a chemistry set.
One seemingly fun but actually incredibly explosive and dangerous experiment is building a rocket. One that's a big improvement over all those lame bottle or water rockets. This can be done in two incredibly stupid and dangerous ways (i.e. don't try these
at home anywhere!):
One (pretty destructive): build a chemical rocket. Your obvious source of fuel would be fireworks, they're already rockets. Just collect a whole bunch of those, take out the thrust fuel and pack it into your own rocket. If your custom rocket would have a metal cylinder to pack the fuel in, any sort of static could trigger an explosion (of packed tightly into the sealed cylinder) or at least a big fire.
Two (extremely destructive): build a 'super water rocket'. Your normal water rocket relies on air pressure in the bottle to push out the water. A bigger bottle can hold more water (so more fuel), and higher air pressure makes the water squirt out faster (more thrust from your fuel), and lock the cork to let the pressure build up. So a seemingly good idea is to get a big, strong container and go for the highest pressure you can possibly get before it launches. So you get some strong metal container, fill it with lots of water, lock the cap in place and increase the pressure. An easy way to increase the pressure is by boiling the water inside it. And then, just when you're about to test the release mechanism, your container explodes. A strong 300 liter (~100 gallon) steel vat with an over-engineered release mechanism should be plenty to level a house. (An article about an unused heating boiler exploding)
Some pretty spectacular home demolition occurs from time to time with chemistry, but it is not kids with their chemistry set, it is "cookers" making drugs in home made laboratories.
The usual cause of the explosion is using ether as a solvent to purify or extract the active ingredients of the drug from the chemical mixture; it is highly volatile, highly flammable and the vapour escaping from the chemistry lab could ignite by moving into another room with an open flame, such as the kitchen with a gas stove, or the basement with a furnace and water heater's pilot lights.
You don't have to be Walter White to get that level of mayhem either. Ordinary people can blow up their houses by taking gasoline powered devices such as lawn mowers, generators or motorcycles into the house for the winter without draining the fuel tanks. The gasoline vapours are heavier than air, and if they escape from the tank due to a defective gas cap, they flow down to the basement where an ignition source is waiting.
The reason that ether or gasoline makes such a huge "boom" is they are well mixed with air by the time they reach the furnace pilot light, otherwise you would get a rather spectacular fire instead. This is the same principle as fuel air explosives use to crush bunkers, or "heaving" explosions of coal dust in a mine or flour dust in a silo.
So your kids might either serendipitously be playing with the chemistry set when Dad's motorcycle causes an explosion, or they may be very early "tweakers" looking to make some sort of psychosomatic drugs (for a certain value of "kid").