Chemistry Past Paper PDF

UNIT 1: What is thermodynamics? It is a branch of physics that deals with heat, work, temperature and their relation to energy and the physical properties. The behaviour of these materials is governed by the 4 laws of thermodynamics. What is bioenergetics? It refers to the concept of energy flow th...

UNIT 1: What is thermodynamics? It is a branch of physics that deals with heat, work, temperature and their relation to energy and the physical properties. The behaviour of these materials is governed by the 4 laws of thermodynamics. What is bioenergetics? It refers to the concept of energy flow through living systems (example ATP). Some terminology: Isolated system → no energy in and no energy out thanks to a boundary. Open systems → energy is transferred to the surroundings, for example a flask of hot coffee transfers heat and it cools, water vapour can escape. Closed system → it transfers energy as it cools but no water vapour escapes. Heat→ is the energy transferred to the surroundings as a result of temperature difference, energy can pass from a warmer body to a colder body. The quantity of heat is q and it depends on how much the temperature is to be changed, the quantity of the substance and its nature. It can also change a state of matter. Calories → is the quantity of heat required to change the temperature of one gram of water by one degree celsius, is a small unit of energy. Heat capacity → is the quantity of heat required to change the temperature of a system by one degree is called the heat capacity of a system. C=q/deltaT Delta T= final temperature-initial temperature Unit (J°C-1 or JK-1) Molar heat capacity (Cp,m) → is the quantity of heat required to raise the temperature of one mole of a substance by one degree. The constant pressure specific heat capacity is called the specific heat, is the quantity of heat required to change the temperature of one gram of a substance by one degree at constant pressure. What are heats of reactions and calorimetry? In the graphic we can see solid lines that indicate the initial temperature and the maximum and minimum that it can reach in an isolated system in an exothermic and endothermic reaction. The broken lines represent pathways to restoring the system to the initial temperature. The heat of reaction is the heat lost or gained by the system in this restoration. Endothermic reactions: (feel cold because they absorb heat from the environment) dissolving salt in water, photosynthesis, cooking an egg, baking bread, water evaporation. Exothermic reactions: (releases heat and has a negative standard) water and acid reactions, campfire, rusting, nuclear fission and freezing water into ice. Ideal Gas Law: PV=nRT It represents the homogenous mixture of gas which sets variables of that gas’s pressure P times volume V equal to the amount in moles n of that gas multiplied by the ideal gas constant R multiplied by its temperature T. Zero Law of Thermodynamics: It establishes the concept of temperature: if two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. Examples of the car, house and office. First Law of Thermodynamics: It is known also as the law of conservation of energy, it states that the energy of a system may change forms but is neither created nor destroyed. Also defined as the internal energy of a system (sum of heat flow and work done on a system deltaE=Q+W). Example: the energy of a child on a swing is always the same, even if it changes from kinetic to potential and vice versa. Any energy entering the system carries a positive sign, thus if the heat is absorbed by the system, q>0, if work is done on the system w>0. Any energy leaving the system carries a negative sign, thus system q