Question 1: Chemical energy is stored in the bonds between atoms within a substance. When a chemical reaction occurs, this stored energy can be released or absorbed, often in the form of heat or light.

Answer: Chemical energy is stored in chemical bonds and released during reactions.

Question 1: Define chemical energy in the context of energy stores.

Answer: Chemical energy is the potential energy stored in the bonds of chemical substances.

Question 2: Explain how the chemical energy in fuels like petrol is converted into useful energy in a car engine.

Answer: Chemical energy in petrol is released during combustion, producing heat that drives the engine's pistons to generate mechanical energy.

Question 1: Calculate the amount of chemical energy released when 2 kg of methane (CH₄) undergoes complete combustion. The molar enthalpy change for methane combustion is -890 kJ/mol. (Molar mass of CH₄ = 16 g/mol)

Answer: 1112 kJ

Question 2: If a battery has a chemical energy store of 500 kJ and supplies 50 kJ of energy in 10 seconds, what is its average power output? Show your working.

Answer: 5 kW

Question 1: Describe a simple experiment to demonstrate the release of chemical energy from a carbohydrate such as glucose. Include the key variables and safety precautions.

Answer: A possible experiment involves burning a known mass of glucose in a calorimeter to measure heat released. Variables include mass of glucose (independent), temperature change (dependent), and oxygen supply. Safety precautions include using heat-resistant gloves, ensuring proper ventilation, and handling fire-resistant materials.

Question 1: A piece of charcoal weighing 100 g releases approximately 30 MJ of energy when fully burnt. Calculate the energy released per gram of charcoal. How might this information be useful in industry?

Answer: 300 kJ per gram; useful for estimating fuel requirements in industries such as power generation.

Question 2: A chemical process involves the combustion of a fuel that releases 500 kJ of energy per kilogram. If a device requires 2.5 MJ to operate, how much fuel (in kg) is needed? Show your working.

Answer: 5 kg

Question 1: Explain the process by which chemical energy stored in food is transferred into the human body, including the role of digestion and respiration. (6 marks)

Answer: Chemical energy in food is broken down during digestion into simpler molecules. These molecules undergo cellular respiration in the mitochondria, releasing chemical energy as ATP, which powers bodily functions.

Question 2: A fuel cell converts chemical energy directly into electrical energy. Describe how this process differs from combustion in terms of energy efficiency and emissions.

Answer: Fuel cells are more efficient as they convert chemical energy directly into electricity with less heat loss and produce fewer pollutants compared to combustion.

Question 1: Describe how chemical energy stored in batteries is used to power electric vehicles. Include considerations of efficiency and environmental impact.

Answer: Batteries store chemical energy which is converted into electrical energy to power motors in electric vehicles. This process is generally efficient and produces no tailpipe emissions, reducing environmental impact compared to fossil fuels.