Why do heat engines all involve combustion? select all that apply. combustion unlocks a huge amount of energy trapped in carbon-hydrogen bonds. combustion does not require any activation energy to react. combustion is highly efficient at converting internal energy into mechanical energy. combustion has a fuel source that is very sustainable. when fuel is combusted it has the ability to convert into mechanical energy to do work, like move a piston.

Combustion unlocks a huge amount of energy trapped in carbon-hydrogen bonds.

Combustion is highly efficient at converting internal energy into mechanical energy.

When fuel is combusted it has the ability to convert into mechanical energy to do work, like move a piston.

Explanation:

Let's analyze the options:

Combustion unlocks a huge amount of energy trapped in carbon-hydrogen bonds. True, combustion is the process where hydrocarbons react with oxygen to create carbon dioxide, water, and heat. And as we know, heat is energy.

When fuel is combusted it has the ability to convert into mechanical energy to do work, like move a piston.

When fuel is combusted, the energy expands the air surrounding the fuel, and this expansion is used as mechanical energy, for example with this expansion you can move a piston.

Combustion is highly efficient at converting internal energy into mechanical energy.  

True, combustion is very efficient to transform the energy in the fuel into heat, and then into internal energy, is not an ideal efficiency, but us a good efficiency