Energy due to position or composition (stored energy) Energy is the capacity to do work or transfer heat. Energy Kinetic energy (EK) Potential energy (EP) Energy due to motion KE= ½ mv2 Energy due to position or composition (stored energy)

Law of Conservation of Energy: the total energy of the universe is constant and can neither be created nor destroyed; it can only be transformed. Energy can be changed from one form to another. Energy can be transferred from one object to another.

Systems & Surroundings A system is the part of the world we want to study (e.g. a reaction mixture in a flask) The surroundings consist of everything else outside the system SYSTEM CLOSED OPEN ISOLATED

e.g. kettle heats on a gas flame HEAT is the energy that transfers from one object to another when the two things are at different temperatures and in some kind of contact e.g. kettle heats on a gas flame cup of tea cools down (loses energy as heat) Thermal motion (random molecular motion) is increased by heat energy i.e. heat stimulates thermal motion Temperature reflects the thermal motion of particles in a substance and indicates the direction in which heat energy will flow.

Three Units Used for Temperature K= Kelvin °C= Celsius °F= Fahrenheit

UNITS OF ENERGY S.I. unit of energy is the joule (J) Heat and work ( energy in transit) also measured in joules 1 kJ (kilojoule) = 103 J Calorie (cal): 1 cal is the energy needed to raise the temperature of 1g of water by 1oC 1 cal = 4.184 J 1 Cal= 1000 cal

Exothermic Reactions -Reactions that give off energy to the surroundings as they progress -Some of the potential energy stored in the chemical bonds is converted to thermal energy (random KE) through heat -Products are generally more stable (stronger bonds) than reactants

Endothermic Reactions -Reactions in which energy is absorbed from the surroundings -Energy flows into a system to increase the potential energy of the system -Products are generally less stable (weaker) than reactants

Energy Direction and Sign: Every energy measurement has three parts: A unit (usually Joules or calories) A number (how many) A sign to tell you direction Signs (+/-) will tell you if energy is entering or leaving a system + indicates energy enters a system (endothermic) - indicates energy leaves a system (exothermic)

endothermic process (positive) Vaporisation Energy has to be supplied to a liquid to enable it to overcome forces that hold molecules together endothermic process (positive) Melting Energy is supplied to a solid to enable it to vibrate more vigorously until molecules can move past each other and flow as a liquid endothermic process (positive) Freezing Liquid releases energy and allows molecules to settle into a lower energy state and form a solid exothermic process (negative) (we remove heat from water when making ice in freezer)

SPECIFIC HEAT: The quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin). q = m x s x DT q- heat in joules. m- mass in grams. s- specific heat capacity in joules per gram per degree Celsius. T-temperature change in Celsius. The symbol Δ means the change in, so ΔT means the change in temperature or T final – T initial