Explanation

Standard enthalpy change is measured under standard conditions, which are defined as a temperature of 298 Kelvin (25°C) and a pressure of 100 kilopascals (101 kPa). 

Explanation

Specific heat capacity is defined as the amount of heat energy required to raise the temperature of one unit of mass of a substance by one degree Celsius (or one Kelvin)

Explanation

If ΔH < 0, the reaction is exothermic.

This means the reaction releases heat into the surroundings, causing the temperature of the surroundings to increase. 

Explanation

If ΔH > 0, the reaction is endothermic. 

In thermochemistry, ΔH represents the change in enthalpy, which indicates the heat absorbed or released during a reaction.

A positive ΔH value signifies that the reaction absorbs heat from its surroundings, making it an endothermic reaction.

This is because the system (the reaction) gains energy, and the enthalpy of the products is higher than that of the reactants. 

Explanation

Enthalpy is defined as the heat content of a system at constant pressure. 

Common symbols: H

SI unit: joule

In SI base units: kg⋅m2⋅s−2

Explanation

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step in the response, regardless of the specific pathway taken. 

Explanation

The combustion of methane is an exothermic reaction.

This means it releases energy, specifically heat, when it burns.

The reaction involves methane reacting with oxygen to produce carbon dioxide and water, releasing a significant amount of energy in the process. 

Explanation

Bond energy is defined as the amount of energy required to break one mole of a specific type of bond in a gaseous molecule.

It reflects the bond strength—the higher the bond energy, the stronger the bond.

For example, to break all H–H bonds in 1 mole of H₂ gas into individual hydrogen atoms in the gas phase:

H₂(g) → 2H(g)  

Bond energy = 436 kJ/mol

Explanation

• An amphoteric substance can act as either an acid or a base depending on the chemical reaction it is involved in.
• The word "amphoteric" comes from the Greek word "amphi," meaning "both". 

Explanation