Q:

When a bomb explodes, does it momentum remain same?

If, from an aircraft, a bomb is thrown to an object placed at ground and bomb explodes before it hits the object, i.e if it explodes in the middle of its path, does it momentum remain same? 
I knew that law of conservation of momentum can be used when no other forces or agents, except action and reaction, do not act between and among objects. Since in this case many kinds of chemical reactions involve, can we apply law of conservation of momentum in this case? If law of conservation of momentum cannot be applied here, what would happen? Either momentum will increase or it will decrease. But I'm not sure which may occur. Please tell me what may happen and what are the reasons behind it. 
At first I thought momentum will decrease because the mass of particles created after explode of bomb will be near to zero, and the product of velocity with a large value and mass with very small value will give another value which is also near to zero. Later I started to think that my idea is not correct, because the product can be higher if the value of velocity of very small particle becomes so much higher.

A:

UPDATE : The explosion itself conserves linear momentum, regardless of how small the fragments are. If we ignore gravity and air resistance and all other external forces, there is no change in total momentum.  This is because the internal forces all occur in equal and opposite pairs (Newton's 3rd Law).
If we take the external forces into account, then momentum is not conserved.  Even during the brief explosion, the bomb and its fragments are being accelerated downwards by gravity.  Air resistance will also affect different fragments unequally because it depends on the size and speed of the fragments, which are very unlikely to be equal.
However, if we extend "the system" to include the Earth and its atmosphere as well as the bomb and its fragments, then we can again say that momentum is conserved - before, during and after the explosion.  All of the forces which we are taking account of (gravity, air resistance, buoyancy, and the bomb blast pushing fragments apart) are now internal forces, so Newton's 3rd Law again applies.   

ORIGINAL ANSWER :
Neglecting air resistance,  and until any of the fragments of the bomb reach the ground, the centre of mass of the bomb follows the same trajectory as it would if the bomb did not explode - ie part of a parabola.  
Conservation of linear momentum does not apply here because there is an outside force (gravity) which changes the magnitude and direction of the total momentum.  However, all of the forces in the explosion are internal forces (action/ reaction) which do not alter the motion of the centre of mass and do not affect total momentum.  
The explosion does not change the total mass of the bomb.   

