Energy and Changes in Matter

Pre-assessment: What do you know about energy and matter Pre-assessment: What do you know about energy and matter? (True or False) 1) The only energy contained by matter is kinetic energy, the energy of the motion of the particles in matter. 2) Temperature and heat are essentially the same quantity.   3) During a change of state (a phase change), the temperature of the system will remain constant until one of the phases disappears. 4) When a chemical system absorbs heat, the heat may be transformed into chemical potential energy in the form of bonds. 5) The process of measuring heat flow between the system and the surroundings is called thermometry. 6) Condensation is an exothermic process. 7) The sum of the kinetic and potential energy with matter is called internal energy. 8) The specific heat capacity of a substance is an extensive property of matter. 9) Changes in heat of a chemical system can be determined by monitoring changes in temperature of the surroundings. 10) If a chemical system absorbs heat, the sign of heat change (q) is positive 

Energy Definition Energy is the ability to do work. (Work = Force x distance) A physical or chemical system that has energy can do work. Energy may be changed from form to form, but the total amount of energy in the universe does not change (Law of Conservation of Energy).

Units of Energy 4.184 J = 1 cal 1000 cal = 1 Calorie SI Unit: joules (J) or kilojoules (kJ) Metric Unit: calorie (cal) (the heat needed to raise 1 gram of water by 1 degree Celsius) Note, a nutritional Calorie is 1000 calories. 4.184 J = 1 cal 1000 cal = 1 Calorie 1 Calorie = 1 kcal 1 kJ = 1000 J 1kcal = 1000 cal

Types of Energy in Matter Nuclear Energy Energy that holds the nucleus (protons and neutrons) of an atom together; represents a lot of stored energy! Kinetic Energy (KE = ½ mv2) Energy that comes from the motion (vibration) of particles; proportional to the absolute temperature (in Kelvin) of the particles. Chemical Potential Energy Energy that is stored in the chemical “bonds” of a substance by virtue of the arrangement of the atoms and molecules. bond

Internal Energy The internal energy (E) of a chemical system is equal to the sum of the kinetic and potential energies of all the particles that make up the system. We cannot measure it directly, but we can measure changes in internal energy. Changes in internal energy are given by the equation: E = q + w where “q” is heat added to or lost by the system and “w” is work done to or done by the system

A simplification… For most chemical situations, the “w” term has a minimal effect on internal energy, and therefore, E = q Basically, the change in the energy of a chemical system is related to the heat flowing into or out of the system. This is easily measured by keeping track of what is happening to the temperature the surroundings! Calorimetry is the technique of measuring the heat exchanged between the system and the surroundings. It is how we know how many Calories are in a Snickers bar!

A Calorimeter

So, “q” is Heat? Heat is energy that flows from a warmer object to a cooler object due to differences in temperature. Temperature is not heat. Temperature is simply a measure of the average kinetic energy of particles of matter. Changes in heat are calculated by the equation: q = mcDT “m” is the mass of the object or substance “c” is the specific heat capacity of the substance “DT” is the change in temperature (Tf – Ti) So, you can see that heat is dependent on these 3 factors, including mass. Heat is extensive!

The Sign of “q” If heat flows into a system from the surroundings, qsystem>0 or positive. (Endothermic process) If heat flows out of a system to the surroundings, qsystem<0 or negative. (Exothermic process) “q” can be calculated for both physical and chemical changes of matter! (as you know)

Specific Heat Capacity (c) The amount of heat required to increase the temperature of one gram of a pure substance by one degree Celsius. Basically, it tells you how well a substances absorbs or retains heat. (Specific heat capacity is intensive.) Units are J/gC or J/gK Substance Specific heat capacity (J/gC) Ice 2.077 Water 4.184 Steam 2.042 Aluminum 0.897 Salt (NaCl) 0.865 Iron 0.449 Mercury 0.139 Silver 0.235

So how does heat come out of matter So how does heat come out of matter? Or, if matter absorbs heat, where does it go? If matter releases heat, it comes from the kinetic energy of the particles (thereby decreasing the motion of the particles) or from the release of chemical potential energy stored in bonds. If matter absorbs heat, it is transformed into kinetic energy (thereby increasing the energy of the motion of particles) or chemical potential energy (bond energy).

Post-assessment: What do you know about energy and matter Post-assessment: What do you know about energy and matter? (True or False) 1) The only energy contained by matter is kinetic energy, the energy of the motion of the particles in matter. F 2) Temperature and heat are essentially the same quantity. F   3) During a change of state (a phase change), the temperature of the system will remain constant until one of the phases disappears. T 4) When a chemical system absorbs heat, the heat may be transformed into chemical potential energy in the form of bonds. T 5) The process of measuring heat flow between the system and the surroundings is called thermometry. F 6) Condensation is an exothermic process. T 7) The sum of the kinetic and potential energy with matter is called internal energy. T 8) The specific heat capacity of a substance is an extensive property of matter. F 9) Changes in heat of a chemical system can be determined by monitoring changes in temperature of the surroundings. T 10) If a chemical system absorbs heat, the sign of heat change (q) is positive. T