C7.1.6 PAG6: Investigating Energy Changes

• What is enthalpy defined as?

  Total energy content
• An endothermic reaction absorbs energy from the surroundings.


  True
• Give an example of an exothermic reaction.

  Burning of wood
• In the formula $q =$$mc\Delta T$, \( \Delta T \) represents the change in temperature.


  True
• To heat 50g of water by 10°C, q = 50 \times 4.18 \times 10 = 2090 \text{ J}</latex>, the value of \( q \) is 2090 J.
• What does the symbol \( c \) in the formula $q =$$mc\Delta T$ represent?


  Specific heat capacity
• What is specific heat capacity measured in?

  J/g°C or J/gK
• What does 'c' represent in the formula q = mcΔT?

  Specific heat capacity
• Specific heat capacity depends on both the mass and the material of the substance.

  False
• The instrument used in calorimetry to measure temperature change is called a calorimeter.
• Match the thermometer type with its advantage:

  Mercury-in-glass ↔️ Inexpensive

  Digital ↔️ High accuracy

  Thermocouple ↔️ Very fast response
• What does 'ΔH' stand for in chemical reactions?

  Enthalpy change
• An endothermic reaction releases heat into the surroundings.

  False
• What is the formula for calculating enthalpy change (ΔH)?

  q = mcΔT
• The specific heat capacity (c) is measured in J/g°C.

  True
• If 50 g of water increases in temperature by 10°C, the enthalpy change is 2090 J
• An exothermic reaction releases energy and results in a negative
• Match the reaction type with the correct energy change:

  Exothermic ↔️ Energy released

  Endothermic ↔️ Energy absorbed
• Specific heat capacity is the energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius.
• What are the units for specific heat capacity?

  J/g°C
• The ΔH for an exothermic reaction is always positive.

  False
• Steps to calculate energy changes using specific heat capacity:

  1️⃣ Identify the mass of the substance

  2️⃣ Determine the specific heat capacity

  3️⃣ Measure the change in temperature

  4️⃣ Apply the formula $q =$$mc\Delta T$

  5️⃣ Calculate the energy change
• The formula for calculating heat absorbed or released is q = mcΔT
• Unlike heat capacity, specific heat capacity depends on the material only.
• What is the experimental technique used to measure heat changes in chemical reactions?

  Calorimetry
• The formula used in calorimetry to calculate heat absorbed or released is q = mcΔT.


  True
• Steps in a calorimetry experiment

  1️⃣ Measure the initial temperature of the reactants

  2️⃣ Mix the reactants

  3️⃣ Monitor the temperature change

  4️⃣ Calculate the heat absorbed or released
• If ΔH < 0, the reaction is exothermic.
• If 50 g of water increases in temperature by 10°C, what is the enthalpy change (ΔH)?

  2090 J
• In the enthalpy change formula, 'q' represents the heat absorbed or released
• What does a negative ΔH indicate about a reaction?

  Exothermic
• Match the type of reaction with its energy change:

  Exothermic ↔️ Energy released

  Endothermic ↔️ Energy absorbed
• What is specific heat capacity?

  Energy to raise 1g by 1°C
• Steps in a calorimetry experiment

  1️⃣ Measure the initial temperature of the reactants

  2️⃣ Mix the reactants and monitor the temperature change

  3️⃣ Calculate the heat absorbed or released
• The heat absorbed or released in calorimetry is calculated using q = mcΔT.

  True
• When 20 g of water cools from 30°C to 20°C, the heat released is -836 J
• What is the unit for specific heat capacity?

  J/g°C
• The formula for calculating enthalpy change is ΔH = q / m = c ΔT
• Match the component with its symbol and units:

  Heat absorbed or released ↔️ q, J

  Mass ↔️ m, g

  Specific Heat Capacity ↔️ c, J/g°C
• What does a negative ΔH indicate about a reaction?

  Exothermic