Science 7 – Unit C: Heat and Temperature Topic 5: The Particle Model and Changes of State

Specific Heat Capacity The S.H.C. is a measure of how much heat a material can hold before its temperature changes. The S.H.C. is a measure of how much heat a material can hold before its temperature changes. Specifically, S.H.C. – the amount of thermal energy that is needed to warm or cool 1g of a material by 1°C. Specifically, S.H.C. – the amount of thermal energy that is needed to warm or cool 1g of a material by 1°C.

Example of Specific Heat Capacity For example, the specific heat capacity of water is 4.13 kJ. That means to raise or lower the temperature of water by 1 K (or 1°C) you need to add or remove 4.13 kJ for every gram of water. For example, the specific heat capacity of water is 4.13 kJ. That means to raise or lower the temperature of water by 1 K (or 1°C) you need to add or remove 4.13 kJ for every gram of water. Mercury, a liquid metal, only has a S.H.C. of 25 J. This means that only 25 J is needed to heat 1 g of the metal 1 k. Mercury, a liquid metal, only has a S.H.C. of 25 J. This means that only 25 J is needed to heat 1 g of the metal 1 k.

The Importance of S.H.C. Water has a high S.H.C. Because it can absorb and store so much heat it has allowed the temperature on Earth to remain pretty consistent over the last 4 billion years. Water has a high S.H.C. Because it can absorb and store so much heat it has allowed the temperature on Earth to remain pretty consistent over the last 4 billion years. In fact, cities which are near oceans (eg. Vancouver often experience cooler summers and milder winters than cities far away from the ocean which experience an extreme range of temperatures (eg. Winnipeg). In fact, cities which are near oceans (eg. Vancouver often experience cooler summers and milder winters than cities far away from the ocean which experience an extreme range of temperatures (eg. Winnipeg).

Heat Capacity While specific heat capacity tells us about how much heat a MATERIAL can store. Heat capacity tells us about how much heat an object can store. While specific heat capacity tells us about how much heat a MATERIAL can store. Heat capacity tells us about how much heat an object can store. Heat capacity depends on two things: Heat capacity depends on two things: –1. The material that make up the object. –2. How much mass the object has. *Remember with S.H.C. the mass is always set to 1 g.

States of Matter

Changes of State

Melting and Boiling Points Melting and Boiling Points A phase change occurs when the temperature drops or rises to a point when the particles in a substance become rearranged. A phase change can also occur when the pressure rises or drops enough. A phase change occurs when the temperature drops or rises to a point when the particles in a substance become rearranged. A phase change can also occur when the pressure rises or drops enough. The melting point is the temperature when a material goes from solid>liquid or liquid>solid. The melting point is the temperature when a material goes from solid>liquid or liquid>solid. The boiling point is the temperature when a material goes from gas>liquid or liquid>gas. The boiling point is the temperature when a material goes from gas>liquid or liquid>gas.

The melting and boiling points of Most Liquids and Gases Most gases have really low boiling and melting points, meaning to get them to turn into a liquid, you have to greatly lower their temperature. (eg. B.P. for oxygen = - 218°C) Most gases have really low boiling and melting points, meaning to get them to turn into a liquid, you have to greatly lower their temperature. (eg. B.P. for oxygen = - 218°C) Most solids such as metals have really HIGH boiling and melting points (eg. M.P for gold = 1054°C) Most solids such as metals have really HIGH boiling and melting points (eg. M.P for gold = 1054°C)

Hidden Heat Remember that when the material changes state (called a phase change), the energy is going into changing the bonds between the particles, not into speeding up or slowing down the particles’ motion. Remember that when the material changes state (called a phase change), the energy is going into changing the bonds between the particles, not into speeding up or slowing down the particles’ motion. This is why the temperature doesn’t change during this time, and you get the plateau in the heat curve. Scientists call this energy that doesn’t heat up the substance ‘hidden heat.’ This is why the temperature doesn’t change during this time, and you get the plateau in the heat curve. Scientists call this energy that doesn’t heat up the substance ‘hidden heat.’

Phase Change Diagram B – the point when the substance first starts melting. B – the point when the substance first starts melting. C – the point where the substance is now completely a liquid. C – the point where the substance is now completely a liquid. D – the point where the substance first starts vaporizing. D – the point where the substance first starts vaporizing. E – the substance is now entirely a gas. E – the substance is now entirely a gas.

Evaporation and Evaporative Cooling In a liquid, the faster moving particles at the surface of the liquid can sometimes escape into the air as a gas particle. In a liquid, the faster moving particles at the surface of the liquid can sometimes escape into the air as a gas particle. As the higher energy particles continue escaping, the AVERAGE THERMAL ENERGY of the liquid (what do we call that again?) drops and the remaining liquid is now cooler. This phenomenon is called evaporative cooling. As the higher energy particles continue escaping, the AVERAGE THERMAL ENERGY of the liquid (what do we call that again?) drops and the remaining liquid is now cooler. This phenomenon is called evaporative cooling.