The properties of matter can best be explained using a model in which all materials are composed of tiny particles (atoms, molecules and ions). There is empty space between particles and particles are constantly moving (their speed is changed by temperature).
A reaction is exothermic if Δ<em>H</em> (or
in some textbooks) is negative:
- H₂ + Br → 2 HBr, ΔH < 0.
- CH₄ + 2 O₂ → CO₂ + 2 H₂O, ΔH < 0.
A reaction is endothermic if Δ<em>H</em> is positive:
- 2 NH₃ → N₂ + 3 H₂, ΔH > 0.
- 2 HCl → H₂ + Cl₂ ΔH > 0.
<h3>Explanation</h3>
The enthalpy of a system is the sum of its internal energy. ΔH < 0 indicates that the reactants lose internal energy in the reaction. Energy conserves, and those internal energies must have converted to some other form of energy. They typically end up as thermal energy. The reaction will release heat since it is exothermic.
Similarly, ΔH > 0 indicates that the reactants gains internal energy in the reaction. Energy conserves. As a result, the reaction must have gained energy from its surroundings. The reaction will be endothermic since it absorbs heat.
Answer : The final volume of balloon will be, 3.35 L
Explanation :
Boyle's Law : It is defined as the pressure of the gas is inversely proportional to the volume of the gas at constant temperature and number of moles.

or,

where,
= initial pressure = 789 mmHg
= final pressure = 632 mmHg
= initial volume = 2.68 L
= final volume = ?
Now put all the given values in the above equation, we get:


Therefore, the final volume of balloon will be, 3.35 L
The answer to this question is A) The box will not move.
Answer:
It's Al 3+ + 3e - → Al
Explanation:
Because three negatively charged electrons are needed to balance the three positive charges on the aluminum ion