Question

If a reaction causes 25.0 g of water to decrease temperature by 4.7 C at constant pressure, what is the change in enthalpy for the reaction? (The specific heat capacity of water is 4.184 J/g oC).

Answer 1

The change in enthalpy for the reaction that caused 25.0 g of water to decrease in temperature by 4.7 °C is -0.49217 kJ, indicating that the reaction is exothermic.

Step-by-step explanation:

If a reaction causes 25.0 g of water to decrease temperature by 4.7 °C at constant pressure, the change in enthalpy (ΔH) of the reaction can be calculated using the formula ΔH = m∙c∙ΔT.

Here, 'm' is the mass of the water, 'c' is the specific heat capacity of water, and ΔT is the temperature change of water.

Given:

- Mass of water (m) = 25.0 g

- Specific heat capacity of water (c) = 4.184 J/g°C

- Temperature change (ΔT) = -4.7 °C (negative because temperature is decreasing)

Thus, the change in enthalpy (ΔH) is:

ΔH = m∙c∙ΔT

ΔH = 25.0 g ∙ 4.184 J/g°C ∙ (-4.7 °C)

ΔH = -492.17 J, which can be converted to kilojoules: ΔH = -0.49217 kJ (since 1 kJ = 1000 J).

Since the temperature decreased and the enthalpy change is negative, the reaction is exothermic, meaning it released heat to the surroundings.