Heat Changes in Temperature and Phase Specific Heat Capacity

1. Heat Changes in Temperature and Phase

2. Specific Heat Capacity • Specific heat capacity – the quantity of energy needed to raise the temperature of 1 kg of a substance by 1°C at constant pressure • How much energy is needed to change the temperature of something • Different for every substance • Specific heat capacity = energy transferred as heat / (mass * change in temperature) • cp = Q/(mΔT) • The subscript p means that the pressure is constant • We will assume this during our calculations • Q = mcΔT

3. Specific Heat Capacity • When the temperature increases, ΔT and Q are positive • When the temperature decreases, ΔT and Q are negative • T can be in either °C or K • 1°C is the same as 1K • Q is in Joules • c is in J/(kg*°C ) or J/(kg* K)

4. Specific Heat Capacity

5. Specific Heat Capacity • To determine a specific heat capacity, you must compare the unknown substance to a known substance such as water • The energy absorbed or lost by the water must be equal to the energy absorbed or lost by the unknown • Calorimetry – an experimental procedure used to measure the energy transferred from one substance to another as heat • The container of the unknown is called a calorimeter • Qw = -Qx • cp,wmwΔTw = -cp,xmxΔTx

6. Latent Heat • Phase change – the physical change of a substance from one state (solid, liquid, or gas) to another at constant temperature and pressure • Energy is required for a change of state • Must be added to go to a higher energy state (gases, plasmas) • Released when moving to a lower energy state (solids)

7. Latent Heat • This energy changes the internal energy of the substance not the temperature • Temperature will not change until all of the substance has completely undergone the phase change

8. Latent Heat • Heat is the energy that is exchanged between two objects at different temperatures or between two objects at the same temperature when one of them is undergoing a phase change • Atoms and molecules prefer to maintain a distance from similar atoms or molecules that correspond to a minimum potential energy

9. Latent Heat • As heat is added to a substance its particles increase in energy • Once enough energy has been added, bonds holding the atoms or molecules break • Resulting in phase changes or chemical reactions if enough energy is added

10. Latent Heat

11. Latent Heat

12. Latent Heat • Energy required to melt a substance goes into rearranging the molecules of that substance • Heat of fusion – the energy per unit mass transferred in order to change a substance from solid to liquid or from liquid to solid at constant temperature and pressure

13. Latent Heat

14. Latent Heat • Energy required to vaporize a substance mostly goes into separating the molecules • Heat of vaporization – the energy per unit mass transferred in order to change a substance from liquid to vapor or from vapor to liquid at constant temperature and pressure • Latent heat – the energy per unit mass that is transferred during a phase change of a substance

15. Latent Heat

16. Latent Heat • Energy transferred as heat during a phase change = mass * latent heat • Q = mL • Lf – latent heat of fusion • Lv – latent heat of vaporization

17. Latent Heat