a toy car starts at the top of a ramp, rolls down and slows to a stop which act most brings the car to a stop

Why does his teacher ask him to balance the equation by including the correct coefficient

Which of the following is most likely true about water in chemical solutions?

Butane gas reacts with oxygen gas to give carbon dioxide gas and water vapor (gas). if you mix butane and oxygen in the correct stoichiometric ratio, and if the total pressure of the mixture is 390 mmhg, what is the pressure (in mmhg) of water vapor after the reaction is completed (temperature and volume do not change).