Match each vocabulary word with its definition.
1. a reaction that absorbs energy
exothermic
2. a reaction that releases energy
enthalpy
precipitate
3. the heat added to or lost by a system at constant pressure
the solid formed as a result of a chemical reaction involving
solutions
endothermic
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Explanation:

1) A reaction that absorbs energy  is called endothermic.

Endothermic reactions:

The type of reactions in which energy is absorbed are called endothermic reactions.

In this type of reaction energy needed to break the bond are higher than the energy released during bond formation.

For example:

C +  H₂O  + 131 kj/mol  →  CO  + H₂

2) A reaction that releases energy is called exothermic.

Exothermic reaction:

The type of reactions in which energy is released are called exothermic reactions.

In this type of reaction energy needed to break the bonds are less than the energy released during the bond formation.

For example:

Chemical equation:

C + O₂   →  CO₂ + 393 Kj/mol

3) The heat added to or lost by a system at constant pressure is enthalpy of system.

Enthalpy is thermodynamic property. It is represented by " H". Its units are joule and calories.

Instead of enthalpy change in enthalpy is measured.

Formula:

ΔH = E + PV

ΔH  = change in enthalpy

E = energy

P = pressure

V = Volume

It give us the information about reaction whether it is exothermic or endothermic.

4) The solid formed as a result of a chemical reaction involving

solutions is called precipitate.

The formation of solid particles during reaction is called precipitation. For example, when we mix silver nitrate and sodium chloride in water silver chloride precipitate out as solid particles.

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.