1. Temperature Increase: Adding heat increases the kinetic energy of the particles within the substance. This causes the particles to move faster, leading to a rise in temperature.

2. Phase Changes: Heat can induce phase changes within a substance. For instance, heat can convert solid ice into liquid water and further to water vapor as it melts and evaporates. Conversely, removing heat can cause substances to solidify or liquefy.

3. Thermal Expansion: Most substances expand when heated. As temperature increases, the particles gain more energy and occupy a larger volume, resulting in expansion. The extent of expansion depends on the material and its properties.

4. Chemical Reactions: In some cases, adding heat can trigger chemical reactions. For example, applying heat can initiate the combustion of fuels, where hydrocarbons react with oxygen to produce heat, light, and other products.

5. Changes in Physical Properties: Heat can modify the physical properties of substances. For example, it can affect their color, density, solubility, electrical conductivity, and magnetism.

6. Alteration in Structure: Heat can cause structural changes in substances, particularly at high temperatures. For instance, heating certain solids leads to their transformation into liquids or gases.

7. Gas Pressure and Volume: If heat is added to a gas in an enclosed space, its molecular motion intensifies. This increased kinetic energy causes the gas particles to exert more force on the container's walls, leading to an increase in pressure. Additionally, the volume of the gas may expand as the molecules spread out due to the higher temperature.

It's important to note that the specific effects of heat addition depend on the substance, its properties, and the surrounding conditions.