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chemistry test
| Question | Answer |
|---|---|
| What is an endothermic reaction? | A reaction where heat is absorbed from the surroundings into the system. |
| What is an exothermic reaction? | A reaction where heat is released from the system to the surroundings. |
| In an endothermic reaction, is enthalpy (ΔH) positive or negative? | Positive (ΔH +) |
| In an exothermic reaction, is enthalpy (ΔH) positive or negative? | Negative (ΔH −) |
| In an endothermic reaction, are products higher or lower energy than reactants? | Products are higher in energy than reactants |
| In an exothermic reaction, are products higher or lower energy than reactants? | Products are lower in energy than reactants |
| What is the transition state? | The highest energy point during a chemical reaction. |
| What is the activated complex? | The unstable arrangement of atoms at the transition state. |
| What does the peak of the energy diagram represent? | The transition state / activated complex. |
| What is a catalyst? | A substance that speeds up a reaction by lowering activation energy. |
| Does a catalyst change the energy of reactants or products? | No, it only lowers the activation energy. |
| Which phase changes are endothermic? | Melting, Boiling, Vaporization, Sublimation |
| Which phase changes are exothermic? | Freezing, Condensation, Deposition |
| What kind of changes involve breaking or separating particles? | Endothermic changes |
| What kind of changes involve combining materials/particles? | Exothermic changes |
| What does a heating curve show? | Temperature increasing as energy is added. |
| Order of states on a heating curve | Solid → Melting → Liquid → Vaporization → Gas |
| What happens during the flat parts of a heating curve? | Phase change occurs and temperature stays constant. |
| What does a cooling curve show? | Temperature decreasing as energy is removed. |
| Order of states on a cooling curve | Gas → Condensation → Liquid → Freezing → Solid |
| During cooling, what happens to energy? | Energy is removed from the system. |
| Ice water sitting on a table (ice is the system). Where does heat move? | From the surroundings → to the ice (system). |
| A pan of water heated on a stove (water is the system). Where does heat move? | From the surroundings → to the system (water). |
| What is thermochemistry? | The branch of chemistry that studies the heat evolved or absorbed during chemical reactions or physical processes. |
| What is heat? | A form of energy transferred between two bodies at different temperatures. |
| What does thermochemistry study? | Heat flow. |
| In which direction does heat always flow? | From a higher temperature substance to a lower temperature substance. |
| What is thermal equilibrium? | When two substances reach the same temperature and heat flow stops. |
| What does the law of conservation of energy state? | The total energy of the universe is constant. |
| What does temperature measure? | The average kinetic energy of particles in a sample |
| What is absolute zero? | The lowest possible temperature where particle motion stops. |
| What temperature does water boil at? | 100°C 373.15 K |
| What is room temperature | 23°C 296.15 K |
| At what temperature does water freeze? | 0°C 273.15 K |
| What is absolute zero in each scale? | -273°C 0 K |
| What is a system? | The specific part of the universe being studied. |
| What are the surroundings? | Everything else in the universe outside the system. |
| What is the universe in thermochemistry? | System + surroundings |
| What is an open system? | Heat and matter can be exchanged. |
| Q: What is a closed system? | A: Heat can be exchanged but matter cannot. |
| Q: What is an isolated system? | A: No heat or matter can be exchanged. |
| Q: What are the three states of matter? | A: Solid, Liquid, Gas |
| Q: Which state has the lowest particle movement? | A: Solid |
| Q: Which state has the highest particle movement? | A: Gas |
| Q: What is melting? | A: Solid → Liquid |
| Q: What is freezing? | A: Liquid → Solid |
| Q: What is vaporization (boiling/evaporation)? | A: Liquid → Gas |
| Q: What is condensation? | A: Gas → Liquid |
| Q: What is sublimation? | A: Solid → Gas |
| Q: What is deposition? | A: Gas → Solid |
| Q: As matter goes from solid → liquid → gas, what happens to interparticle distance? | A: It increases |
| Q: What happens to potential energy from solid → gas? | A: It increases |
| Q: What happens to temperature from solid → gas? | A: It increases |
| Q: What happens to kinetic energy from solid → gas? | A: It increases |
| If▲ H is positive (+), is the reaction endothermic or exothermic? | Endothermic (energy is absorbed from the surroundings). |
| If ▲ H is negative (-), is the reaction endothermic or exothermic? | Exothermic (energy is released to the surroundings). |
| In nature, do substances prefer a high or low energy state? | Low energy state (which results in higher stability). |
| On which side of a chemical equation is heat written for an exothermic reaction? | The Product side (because heat is being "produced"). |
| What do the subscripts fus, vap, and sub stand for? | Fusion (melting), Vaporization (boiling), and Sublimation (solid to gas). |
| What is the simplest definition of Entropy (S)? | A measure of the randomness or disorder in a system. |
| Rank the phases of matter from lowest to highest entropy. | Solid (low) < Liquid < Gas (high). |
| Does entropy increase or decrease when a solid is dissolved in water? | Increases (particles become more spread out/disordered). |
| What happens to entropy when the number of moles of gas increases in a reaction? | Entropy increases (▲ S is positive). |
| How does increasing temperature affect entropy? | It increases entropy because the random motion of molecules increases. |
| What does it mean if a process is "spontaneous"? | It occurs without outside intervention (though it might still need activation energy). |
| What is the sign of ▲ G for a spontaneous reaction? | Negative (-). |
| What combination of ▲ H and ▲ S always results in a spontaneous reaction? | Negative ▲ H (exothermic) AND Positive ▲ S (more disorder).What combination of ▲ H and ▲ S will never be spontaneous? |
| What combination of ▲ H and ▲ S will never be spontaneous? | Positive ▲H (endothermic) AND Negative ▲ S (less disorder). |
| If ▲ G = 0, what state is the reaction in? | Equilibrium. |
| If a reaction is Exothermic ▲ H but becomes More Ordered ▲ S, when is it spontanious | at low temp at high temp its not |
Created by:
Fernando.Quezada